Date Difference Calculator

How many days are between two dates? This date difference calculator gives the exact answer in years, months, and days, plus total days, total weeks, total hours, business days, and weekend days. It also adds or subtracts days from a date, so you can find a deadline, a due date, or a date a set number of days in the past. Everything updates instantly, and all of the math runs in your browser.

Counting days by hand is a classic source of off-by-one errors. People forget leap days, miscount month lengths, and disagree about whether the start date and the end date both count. The calculator removes that guesswork by stating its rules plainly: the basic difference counts the days from the start date up to, but not including, the end date, which is the number of midnights between them. Turn on inclusive counting and both end dates count, which adds exactly one day. Business days count Monday through Friday only, with both end dates included when they fall on weekdays, and holidays are never subtracted unless you subtract them yourself, because holiday lists differ by employer, court, and state.

Use this tool for project timelines, notice periods, contract dates, travel planning, school terms, pregnancy timelines, and anniversary counts. The default example compares January 1, 2026, with October 29, 2026, a span of 301 days, so you can see a full result the moment the page loads. The sections below explain inclusive and exclusive counting, business day rules, leap year effects, and the add and subtract mode, with worked examples you can check in the calculator.

How to Use the Date Difference Calculator

Start by picking a mode. Difference mode compares two dates. Add mode moves a date forward. Subtract mode moves a date backward. The default mode is difference, with January 1, 2026, and October 29, 2026, already entered, so the full result is visible the moment the page loads.

1. Pick the mode. Use difference mode for a gap, add mode for a deadline in the future, and subtract mode for a date in the past.
2. Enter the start date and the end date. In difference mode, the order does not change the size of the gap. The calculator tells you which date is earlier. Use the Swap button if you want the earlier date listed first.
3. For add or subtract mode, enter the amount and the unit. Days and weeks are exact counts. Months and years are calendar units, so adding one month to January 31 lands on the last day of February.
4. Tick inclusive counting only when both end dates should count. Leave it unticked for elapsed time, countdowns, and deadlines. Tick it for hotel-style counts, vacation day counts, and schedules where both the first and last day count as days used.
5. Read the business day row for work planning. It counts Monday through Friday, including both end dates when they are weekdays. Weekend days are shown on the next row so you can reconcile the two counts against the inclusive total.

If either date field is blank or impossible, the calculator asks for a valid date instead of guessing. If you enter a negative amount in add or subtract mode, the calculator treats it as zero, because the mode itself already sets the direction. Use the mode to change direction, not a minus sign.

Which Mode Fits Your Question

Most questions fit one mode cleanly. Ask yourself whether you know both dates or only one. If you know both dates and want the gap, use difference mode. If you know one date and a length of time, use add or subtract mode. If you know a deadline and want to count backward to a start date, use subtract mode from the deadline. If you want to count forward from today to a project end, use add mode from today. The days calculator covers the same ground with an emphasis on adding and subtracting whole blocks of days and on counting working days inside a range, so try both tools and use whichever layout fits your question best.

Reading the Headline Result

The headline gives the calendar difference in years, months, and days, which is the form people use in conversation and on forms. The table below it gives the same gap in single units, which is the form people use for planning and for billing. A gap of one year, two months, and three days is also 425 days in a common span, or 60 weeks and 5 days, depending on the exact dates. Always state which form you mean when you share a result, because the two forms look different even though they describe the same gap.

Exclusive and Inclusive Counting Explained

The difference between exclusive and inclusive counting is one day, and it causes more arguments than any other date question. Exclusive counting, the default in this calculator, counts the days strictly between two dates. It answers the question, how many midnights pass from the start date to the end date? From Monday to Tuesday is one day. From January 1 to January 1 is zero days. This is the count used for elapsed time, for age in days, for countdowns, and for most deadlines stated as a number of days from a date.

Inclusive counting counts both end dates as days in the span. From Monday to Tuesday is two days, because both Monday and Tuesday count. From January 1 to January 1 is one day. This is the count used when both days are used, such as a vacation that starts on the first day and ends on the last day, a hotel stay that charges by calendar dates covered, or a course that meets on both the first and last day. Neither count is wrong. They answer different questions, and the mistake is using one when the other was meant.

When a contract, a court order, or a school rule says a number of days, check whether it says inclusive, exclusive, or neither. If it says neither, read the examples in the rule or ask the person who wrote it. In United States legal practice, counting rules vary by court and by rule, and some rules exclude the triggering day and include the last day, while others do the opposite. This calculator shows both counts side by side so you can pick the one your rule requires, and it labels the inclusive setting you chose so the result is never ambiguous.

Midnights, Not 24-Hour Periods

Date differences count calendar days, not 24-hour periods from a time of day. From 11:00 PM on Monday to 1:00 AM on Tuesday is one calendar day of difference, even though only two hours passed. From 1:00 AM on Monday to 11:00 PM on Tuesday is also counted as one day in the exclusive sense, even though 46 hours passed. If you need exact hours between two times of day, use the time calculator, which handles clock times, overnight spans, and breaks. For date-only questions, midnights are the right unit, and daylight saving time never changes the count, because the calculator counts calendar days in Coordinated Universal Time.

Same-Day and Reversed Dates

Same-day pairs give zero exclusive days and one inclusive day, which surprises some people the first time they see it. It is correct: no midnight passes between a date and itself, and one calendar date is covered when both end dates count. Reversed dates, where the end date is earlier than the start date, give the same gap size with a note about direction. The calculator never gives a negative day count for a difference, because a gap is a size, not a direction. If you need a signed result, use subtract mode, which states the direction in words.

Business Days, Weekends, and Holidays

A business day, also called a working day, is a day when most offices, banks, and courts are open. In the United States, that normally means Monday through Friday, excluding federal holidays. This calculator counts business days as Monday through Friday, including both end dates when they are weekdays, and it does not subtract holidays. That choice is deliberate: federal holidays, state holidays, court holidays, and employer holidays all differ, and subtracting the wrong list would silently give the wrong answer for a deadline.

To make a holiday-aware count, take the business day total and subtract the number of holidays in your range that fall on weekdays. Do not subtract a holiday that falls on a weekend, because it was never counted as a business day in the first place. For federal holidays, the official source is the United States Office of Personnel Management schedule, and for court deadlines, the court calendar controls. The National Institute of Standards and Technology maintains the official time standards that underlie these calendar rules, and its time and frequency pages explain how official time is kept in the United States.

• Project planning: use business days for work effort, and calendar days for elapsed time, and keep both numbers in the plan.
• Delivery estimates: a delivery in five business days can take seven calendar days or more, depending on the starting weekday and holidays.
• Notice periods: check whether the rule counts calendar days or business days before you count. A 30-day notice and a 30-business-day notice differ by about two weeks.
• Leave and vacation: some employers count vacation in calendar days and some in business days. Ask payroll which count your balance uses.
• Payroll: a pay period is usually a fixed set of calendar dates, and the business days inside it are what determine scheduled workdays.

Federal Holidays in a Typical Year

The table below lists the federal holidays most employers and courts observe. Dates shift when a holiday falls on a weekend, and the observed date may move to the nearest Friday or Monday. Always confirm the observed date for the year you are counting.

Weekend Rules Around the World

The Monday to Friday business week is standard in the United States, but it is not universal. Some countries and some industries use a Sunday to Thursday week, a six-day week, or a single rest day. If you are counting business days for a team in another country, confirm the local weekend before you count. A span that contains ten business days in the United States can contain a different number under a Sunday to Thursday week, and a holiday list from one country will not match another. This calculator uses the United States Monday to Friday week throughout, and the article states that plainly so international users can adjust the result.

Adding and Subtracting Days, Weeks, Months, and Years

Add and subtract mode is calendar arithmetic, and each unit behaves differently. Days and weeks are exact: adding seven days always moves the date forward by seven calendar days, and adding one week is the same as adding seven days. Months and years are calendar units: adding one month moves the month number forward by one and keeps the day of the month when possible, and adding one year moves the year forward by one and keeps the month and day when possible. When the target month is shorter, the result lands on the last day of the target month.

The month-end snap rule surprises people who expect January 31 plus one month to be March 3, which is what you would get by adding 31 days. Calendar month addition does not work that way. It moves the month first, then fits the day into the new month. March 3 would be the result of adding 31 days, not one calendar month, and the two operations answer different questions. Use days when you mean a fixed length of time, and use months when you mean the same day of the month in the next month.

Adding Business Days to a Date

Adding business days is a separate operation from adding calendar days, and this calculator does not pretend they are the same. To add ten business days to a date by hand, add two calendar weeks, then adjust for the starting weekday and any holidays. As a rough rule, ten business days is fourteen calendar days if you start on a Monday and land on a Friday two weeks later, but it is sixteen calendar days if you start on a Friday and must cross two weekends. The exact count depends on the starting weekday, so always count day by day for a deadline, or use a business day counting method that steps through weekdays only. The days calculator on this site includes a working day counting view that steps through a range and reports business days and weekend days separately.

Repeat Calculations and Series of Dates

Some plans need a series of dates, not a single date: a payment every 30 days, a meeting every two weeks, or a review every three months. The reliable way to build a series is to add the interval to the previous date in the series, one step at a time, using the same unit each time. Adding 30 days repeatedly gives a series that drifts through the month, while adding one calendar month repeatedly keeps the same day of the month, with snaps at month ends. Choose the unit that matches the promise you made. A rent due on the first of each month is a calendar month series. A medication taken every 30 days is a day series. Mixing the two is a common cause of missed dates.

Leap Years and Month Lengths

Every date difference that spans February must respect the leap year rule and the month length table. The Gregorian leap rule is: a year divisible by four is a leap year, except century years, which must also be divisible by four hundred. The year 2024 was a leap year, 2025 and 2026 are not, and 2028 will be. The year 2000 was a leap year, and 2100 will not be. A difference from February 28 to March 1 is one day in a common year and two days in a leap year, because February 29 sits between them in a leap year. That single day has decided contract disputes, so it is worth checking whenever a span crosses February.

A handy memory aid for month lengths is the knuckle method: the raised knuckles are the 31-day months, and the valleys are the shorter months, with February as the special case. A more reliable aid is the rhyme, thirty days hath September, April, June, and November, with February as the exception. Either aid works for a quick check, but for a deadline, use the calculator, because a memory aid that is right nine times out of ten still fails on the tenth.

Why February Has 28 Days

February is short for historical reasons rooted in the Roman calendar, where February was the last month of the year and the month where adjustments were made. When Julius Caesar reformed the calendar, February kept its short length, and the leap day was added to February rather than to a longer month. The Gregorian reform kept that arrangement and refined the leap rule. The result is a calendar that stays lined up with the seasons to within about one day every three thousand years, which is accurate enough for every planning purpose in this article.

Worked Examples for Common Situations

The examples below use real dates and show both the exclusive count and the business day count, so you can see how the two counts diverge over weekends and holidays. Try each one in the calculator to confirm the result.

The leap year row is instructive. A full leap year has 366 exclusive days, one more than a common year, and the business day count rises by one only when the extra day is a weekday. In 2024, February 29 was a Thursday, so the business day count for the full year rose by one compared with a common year starting on the same weekday pattern. In a year where the leap day falls on a weekend, the business day count for the full year would not rise at all, even though the calendar count does. That is another reason to keep calendar days and business days as separate numbers in every plan.

Example: A 30-Day Notice Period

A notice given on October 29, 2026, with a 30-day notice period, expires on November 28, 2026, if the rule counts 30 days from the notice date exclusive of the notice day. If the rule counts inclusively, it expires on November 27, because the notice day itself counts as day one. If the rule counts business days, the expiry is later still, around December 10, depending on holidays. The same notice, three different expiry dates, all correct under different rules. Always read the rule, then pick the matching count in the calculator, and write down which count you used so the other party can check it.

Example: Counting Down to a Trip

A trip that starts on December 20, 2026, counted from October 29, 2026, is 52 days away in the exclusive count. That is seven weeks and three days, or about a month and three weeks in calendar terms. If you need to book flights, hotels, and a passport renewal, work backward from the trip date using subtract mode: subtract eight weeks for a passport renewal, subtract two weeks for hotel booking, and subtract one week for packing and checklists. Each subtraction gives a concrete action date, which is more useful than a single countdown number. The countdown timer is a good companion for the trip itself, because it ticks down in days, hours, minutes, and seconds.

Date Differences in History and Science

Date arithmetic is older than the modern calendar. Astronomers count days with the Julian day number, a continuous count of days from January 1, 4713 BC, which makes differences between distant dates a simple subtraction. Historians count regnal years, calendar eras, and fiscal years, each with its own start date. Scientists counting the age of a sample use years before present, with present fixed by convention to 1950. All of these systems exist because counting days across calendar changes is hard, and a continuous count removes the month and leap year complications. This calculator uses the Gregorian calendar for everyday dates, which is the right choice for modern planning, and it counts in Coordinated Universal Time so daylight saving time never corrupts a result.

The official time scale in the United States is maintained by the National Institute of Standards and Technology, which operates atomic clocks and distributes official time. The National Institute of Standards and Technology explains how atomic time, Coordinated Universal Time, and leap seconds relate to the calendar dates used here. For everyday planning, leap seconds do not matter, because they adjust clock time by one second, not calendar dates. For scientific work that needs sub-second accuracy, the distinction matters, and a specialized time tool should be used.

Calendar Reforms and Old Dates

The Gregorian calendar replaced the Julian calendar in 1582 in Catholic countries, and other countries adopted it over the next three centuries. Britain and its American colonies adopted it in 1752, skipping eleven days in September of that year. Russia adopted it in 1918. Dates before adoption in a given place follow the old calendar, and a date difference that spans an adoption date must account for the skipped days. This calculator does not attempt that historical correction, because every modern planning date falls long after adoption. For family history research that reaches the 1700s or earlier, check the adoption date for the place involved before you trust a difference that crosses it.

Planning With Date Differences

Date differences turn vague plans into dated plans. A project with a start date and a duration gets an end date. A contract with a start date and a term gets an expiry date. A trip with a return date and a booking lead time gets a booking deadline. The discipline is to write down all three pieces for every plan: the start date, the length, and the counting rule. If any piece is missing, two people can follow the same plan and arrive on different dates, each convinced the other is wrong.

• Projects: record the start date, the working day count, the calendar end date, and the holiday list used.
• Contracts: record the start date, the term in days or months, the counting rule, and the expiry date as calculated.
• Travel: record the departure date, the return date, the inclusive night count for hotels, and the booking deadlines.
• School: record the term start, the term end, the break dates, and the exam dates, all as calendar dates.
• Health: record appointment dates, follow-up intervals in days, and medication schedules in days, not months, when precision matters.
• Personal: record anniversaries, birthdays, and milestones as calendar dates, and count down with the exclusive count.

Building a Timeline Backward From a Deadline

Backward planning is the most reliable way to hit a deadline. Start with the deadline date, subtract the longest lead time first, and keep subtracting until you reach today. Each subtraction gives a start date for one piece of work. If a start date falls in the past, the plan is already late, and the deadline or the scope must change. If every start date falls in the future, the plan is feasible, and the earliest start date is the date work must begin. Use subtract mode for each step, and write the result of each step down before you do the next one, so the chain is auditable.

Checking a Timeline Forward

Forward checking is the mirror image. Start with today, add each phase in order, and see where you land. If you land after the deadline, a phase must shrink or overlap with another phase. If you land well before the deadline, you have slack, which can absorb delays. The most useful forward check is the critical path: the chain of phases where any delay delays the whole project. Date differences for the critical path should use business days, because work happens on business days, while the overall elapsed time should use calendar days, because the calendar keeps moving on weekends too.

Comparing This Tool With Related Calculators

Several calculators on this site overlap with date differences, and each one has a natural home. The age calculator answers how old a person is on a date. The days calculator emphasizes adding and subtracting blocks of days and counting working days. The time calculator handles clock times and timesheets. The countdown timer ticks live toward a future date. This date difference calculator is the general-purpose tool: any two dates, any gap, with business days and add and subtract modes in one place.

Using the right tool matters less than using one tool consistently and writing down the counting rule. If a team uses different tools with different default counts, the team will disagree about deadlines even when every tool is correct. Pick one count, state it in every plan, and the tools will agree, because they all count the same calendar.

When to Use Total Hours Instead of Days

Total hours are useful when the work is measured in hours, such as a 40-hour work week, a flight duration, or a lab experiment. For spans longer than a few days, total hours become hard to read, and days and weeks are clearer. A span of 301 days is 7,224 hours, which is exact but unhelpful for planning a vacation. A span of 8 hours is 0.33 days, which is exact but unhelpful for a timesheet. Use the unit that matches the decision: days for calendars, hours for shifts, weeks for projects, and months for contracts.

Date Difference Accuracy and Limits

This calculator is exact for Gregorian calendar dates, counting whole days in Coordinated Universal Time. It handles leap years with the full century rule, month ends with calendar arithmetic, and reversed dates by reporting the gap size with a direction note. Business day counts are exact for the Monday to Friday week, excluding weekends only. The result is as exact as the dates entered. A wrong start date, a guessed cutoff, or a misunderstood counting rule will produce an exact answer to the wrong question, so the inputs and the rule deserve more attention than the arithmetic.

The limits are about holidays, time zones, and history. Holidays are not subtracted, because no single holiday list fits every employer, court, and state. Time of day is ignored, because this is a date tool, not a clock tool; use the time calculator for clock times. Dates before the Gregorian adoption in a given place need historical care. And legal deadlines must always be checked against the exact rule that governs them, because counting rules for courts and contracts vary, and a calculator cannot read a contract for you.

• Exact: calendar difference, total days, weeks, hours, business days for a Monday to Friday week, and add or subtract results for days, weeks, months, and years.
• Needs your input: holiday subtraction, because the holiday list depends on your employer, court, or state.
• Not covered: clock times, time zones, historical calendar changes, and legal interpretations of a specific deadline rule.

Date Differences for School Terms and Work Schedules

School terms and work schedules are built from date differences, and the same span can be described in days, weeks, or months depending on the audience. A school term from September 1 to December 18 is 108 exclusive days, or 15 weeks and 3 days, or about three and a half calendar months. A work project from March 2 to March 13 is 11 exclusive days, or 10 business days, or two work weeks. Each description is correct, and each one serves a different reader: parents think in calendar days, teachers think in weeks, and managers think in business days. The calculator reports all three, so one calculation serves every reader.

For school planning, the age on the cutoff date matters as much as the term length, and the age calculator gives that age exactly. For family planning around a school term, the pregnancy due date calculator gives a due date counted in weeks from a known date, using the same calendar-step method as a date difference. Keeping the tools consistent, with the same counting rules stated each time, prevents a family plan and a school plan from disagreeing by a day.

• Term length: count calendar days for the elapsed span, business days for teaching days, and subtract holidays for instructional days.
• Exam windows: count from the first exam day to the last exam day inclusively, because both days are exam days.
• Work schedules: count business days for scheduled work, and calendar days for the elapsed time a project occupies on the calendar.
• Pay periods: count the calendar dates in the pay period, and the business days inside it, and keep both numbers on the timesheet.
• Leave balances: confirm whether leave is counted in calendar days or business days, because the balance drains at a different rate under each rule.

1. Enter the term or project start date and end date.
2. Read the exclusive day count for elapsed time and the business day count for work time.
3. Subtract weekday holidays to get instructional or working days, if holidays apply.
4. Write all three numbers, labeled, in the plan, so every reader uses the same count.

How to Double-Check Any Date Difference

Every important date difference deserves a second check by a different method. The second method does not need to be fancy. It only needs to be independent, so the same mistake cannot hide in both checks. The three methods below each catch different errors, and together they catch almost every counting mistake a person or a tool can make.

• Count forward and backward: count from the start date to the end date, then count backward from the end date to the start date. The two counts must match.
• Count in blocks: count whole months first, then leftover days, and compare the total with the single-unit day count.
• Check the weekdays: confirm the weekday of each end date, because a wrong weekday usually means a wrong date was entered.
• Check the leap day: if the span crosses February, confirm whether February 29 falls inside the span, and adjust by one day if needed.
• Check the inclusive label: confirm whether the count you need includes both end dates, and compare the exclusive and inclusive rows in the table.

1. Run the calculation once in the calculator and write the result down.
2. Count the span by hand in month blocks, on paper, and compare the two results.
3. If they disagree, check the inputs first, then the counting rule, then the leap day, in that order.
4. Keep the written check with the plan, so a later reader can see how the date was reached.

• Inputs: a mistyped month or year is the most common cause of a large error.
• Counting rule: an inclusive and exclusive mix-up is the most common cause of a one-day error.
• Leap day: a missed February 29 is the most common cause of a one-day error in a span that crosses February.
• Holidays: a holiday subtracted twice, or not at all, is the most common cause of a business day error.

Frequently Asked Questions

How many days are between January 1 and October 29, 2026?

There are 301 exclusive days between them, and 302 inclusive days counting both end dates. The calculator shows both counts, plus 43 weeks exactly, 7,224 hours, and the business day count for the span.

Does the calculator count the end date?

By default, no. The basic difference counts midnights between the dates, so the end date itself is not counted. Tick the inclusive box to count both the start date and the end date, which adds exactly one day to the total.

How are business days counted?

Business days are Monday through Friday, counting both end dates when they fall on weekdays. Weekends are never counted. Public holidays are not subtracted, because holiday lists differ. Subtract weekday holidays in your range from the business day total to make a holiday-aware count.

What date is 30 days from today?

Use add mode, enter 30 days, and set the start date to today. The result date and its weekday appear at once. From October 29, 2026, adding 30 days gives November 28, 2026, a Saturday.

How do I add months to a date?

Use add mode, choose months as the unit, and enter the number of months. Adding one month to January 31 lands on the last day of February, which is February 28 in a common year and February 29 in a leap year.

What if the end date is before the start date?

The calculator reports the same gap size and notes that the end date is earlier. A gap is a size, not a direction, so the count is never negative. Use subtract mode if you need a result stated as moving backward from a date.

Does the calculator handle leap years?

Yes. It uses the full Gregorian rule, including the century exception. A span from February 28 to March 1 is one day in a common year and two days in a leap year, because February 29 falls between them in a leap year.

Can I count days for a contract or court deadline?

You can count the days, but you must check the counting rule that governs the deadline first. Court and contract rules vary on inclusive counting, business days, and holidays. Count with the rule that applies, and keep a note of which count you used.

What is the difference between this tool and the days calculator?

This tool is the general-purpose date difference tool, with difference, add, and subtract modes and business day counts in one place. The days calculator emphasizes adding and subtracting blocks of days, counting working days in a range, and preset jumps such as 30, 60, and 90 days. Both count the same calendar, so they agree when given the same inputs and the same counting rule.

Why do total weeks and total months not multiply back to total days?

Weeks and months are different groupings of the same days. Weeks always divide days by seven, with a remainder. Months group days by calendar month, and months vary from 28 to 31 days, so total months times 30 is only an approximation. The calculator reports each grouping separately so they are never confused.

Disclaimer: This calculator is for general information and planning only. It counts Gregorian calendar days and Monday to Friday business days, excluding holidays. For court, contract, or legal deadlines, check the exact counting rule that applies, because rules vary by court, contract, and state.