Days Between Dates Calculator

A days between dates calculator counts the gap between any two dates in days, weeks, and months. From 1 March 2026 to 1 September 2026 is 184 days, from 15 January 2026 to 15 February 2026 is 31 days, and from 1 January 2026 to 31 December 2026 is 364 days. The days calculator above gives the gap instantly, and this page works through the spans people measure most, from trips to projects to treatment courses.

The gap is the subtraction of the two dates, excluding the start date, and the arithmetic is month by month: the remaining days in the start month, the full months in between, and the days in the end month. A leap day inside the span adds one, and a span that crosses February is the one to check. This page shows five spans worked out, converts them to weeks, and explains the endpoint convention.

How Day Counts Work: Between Dates, Until a Date, and Added Days

A day count is always a subtraction of two dates on the Gregorian calendar, and the only thing that changes between the questions on this page is which dates you subtract. Days between two dates is the gap from the first to the second: 1 March 2026 to 1 September 2026 is 184 days. Days until a date is the same subtraction with today as the start: from 1 November 2026 to 25 December 2026 is 54 days, and to 1 January 2027 is 61 days. Adding days is the same arithmetic in reverse: 1 November 2026 plus 30 days is 1 December 2026, and plus 90 days is 30 January 2027. One tool, three questions, one rule.

Business days are the exception that proves the rule. A business day is a weekday, Monday to Friday, excluding public holidays, so the count from Monday 2 November 2026 to Friday 6 November 2026 is 5 business days out of 5 calendar days, while a span from Friday to the following Monday is 2 business days out of 4 calendar days. The calculator counts weekdays automatically, but holidays vary by state and employer, so treat a business-day count as weekdays unless you have added your own holidays to it.

The calendar behind all of this is the Gregorian calendar, and the official time reference for the United States is published at time.gov. The arithmetic itself is simple once the endpoints are settled: the count excludes the start date and includes the end date, which is the convention used throughout this page and in the calculator above.

Step 1 — Fix the Two Dates

Write the start date and the end date, or today and the target date, as year, month, and day. For a countdown, the start is today: 1 November 2026 to 25 December 2026. For adding days, the start is the date you have and the number of days is the amount to add.

Step 2 — Subtract, or Add, the Days

Subtract the start date from the end date for a gap or a countdown. For adding days, add the number to the start date’s day count and carry the overflow into the next month: 28 February 2026 plus 1 day is 1 March 2026, because February 2026 has 28 days and there is no 29 February.

Step 3 — Adjust for Weekdays if Needed

If the answer must be business days, remove Saturdays and Sundays from the count, and then remove any holidays that fall inside the span. A week always contributes exactly 5 business days, so a 10-business-day span is two full weeks, however the calendar days fall.

Worked Examples: Days Between Dates

Each row gives two dates, the day count between them, and the month-by-month count behind it.

The first row shows the month-by-month count: March has 30 days remaining after 1 March, April has 30, May has 31, June has 30, July has 31, August has 31, and 1 September adds 1, which totals 30 + 30 + 31 + 30 + 31 + 31 + 1 = 184 days. The second row is the short span: 15 January to 15 February is 31 days, because January has 31 days and the span runs from the 15th to the 15th. Try the same dates in the calculator above and confirm each count.

How to Use the Days Calculator

The calculator has three modes: count days between two dates, count days until a date, and add or subtract days from a date. Choose the mode that matches your question, enter the dates, and the answer appears with a breakdown in weeks and months.

1. Choose the mode. Between two dates for a gap, until a date for a countdown, or add days to move a date forward or backward.
2. Enter the dates. Use the date pickers; the default span of 1 January 2026 to 1 January 2027 shows 365 days, and you can move either end to watch the count change.
3. Read the total days. The headline figure is the calendar-day count, excluding the start date, which is the standard convention.
4. Read the weeks and months. The breakdown shows the same span in weeks and in months, which is the form most plans and schedules use.
5. Switch to business days when work is the question. The weekday count is the number that decides deadlines, delivery estimates, and leave balances.

The Same Gap in Days, Weeks, and Months

A gap is more useful when it is expressed in the unit your plan uses. This table converts the example spans into all three forms.

Common Mistakes With Day Counts

Day counts go wrong in a handful of predictable ways. These are worth checking before you book, file, or promise anything.

• The off-by-one error. Counting both endpoints, or neither, shifts the answer by a day. The standard count excludes the start date.
• Forgetting leap years. A span crossing 29 February is a day longer than a month-by-month estimate suggests, and the error only shows up in leap years.
• Treating business days as calendar days. Five business days from a Friday is the following Friday, not the following Wednesday, because the weekend sits in between.
• Adding days across a month boundary by hand. Adding 30 days to 1 November gives 1 December, not 31 November, which does not exist; carrying into the next month is where hand counts slip.
• Using today when the question means another date. A countdown from 1 November to Christmas is 54 days; from 2 November it is 53. The start date is part of the answer.

Where You Will Use a Day Count

Counting days is the quiet arithmetic behind plans, deadlines, and celebrations, and it appears in more places than most people notice.

• Countdowns. Days until a holiday, a wedding, a product launch, or a holiday trip turn a vague wait into a number you can watch fall.
• Deadlines. A report due in 30 days and a filing due in 90 days are different dates, and only the day count tells you which calendar date each one lands on.
• Travel. The days between departure and return decide the length of the trip, the hotel nights, and the insurance cover.
• Health. Treatment courses, recovery periods, and pregnancy dates are all counted in days and weeks from a start date.
• Work planning. Business-day counts decide how many working days a project has, which is the number that determines whether a deadline is realistic.

Gaps People Measure Most

The gaps people count are usually tied to a plan: a trip, a project, a course of treatment, or a wait for an answer. A trip from 1 March to 1 September is 184 days, which is 26 weeks and 2 days, and a project from 15 June to 1 November is 139 days, which is 19 weeks and 6 days. For work, the business-day count is the number that matters, and a 139-day span contains about 99 weekdays, depending on where the weekends fall. The calculator above gives the calendar count, and the business-day count follows from the weekdays inside the span.

Tips for Accurate Results

Day arithmetic is exact, so accuracy comes from settling the endpoints and the convention before you count.

1. Write both dates down. A count without its endpoints cannot be checked, and the endpoints are where most errors start.
2. Confirm the leap year. If the span crosses February, check whether the year is a leap year before trusting a hand count.
3. Use the calculator for month crossings. Adding days across a month boundary is the most error-prone hand calculation in this whole topic.
4. Say whether weekends count. “In 10 days” and “in 10 business days” are different promises, and the difference is a whole weekend.
5. Recheck long spans by splitting them. Count a long span in two halves and add the halves; if they do not sum to the whole, one half is wrong.

Days Quick Answers

These are the day counts people look up most often, each one verified against the calculator above.

Related tools on this site: the main days calculator, date difference calculator, age calculator, countdown timer, and the days calculator again whenever you need a fresh check.

Frequently Asked Questions

How many days are between 1 March and 1 September 2026?

There are 184 days. Counting month by month: 30 remaining days in March, 30 in April, 31 in May, 30 in June, 31 in July, 31 in August, and 1 in September, which totals 184 days.

How do I calculate days between two dates?

Subtract the start date from the end date, excluding the start date. Add the remaining days in the start month, the full months in between, and the days in the end month, plus one for each 29 February in the span. The calculator above does the count instantly.

How many days are between 15 January and 15 February 2026?

There are 31 days, because the span runs from the 15th of one month to the 15th of the next, and January has 31 days. A span from the 15th to the 15th always equals the length of the first month.

What is the difference between calendar days and business days?

Calendar days count every day, including weekends, while business days count only Monday to Friday. A 7-day span is 5 business days if it runs Monday to Friday, and 2 business days if it runs Friday to Monday.

Can the calculator count past dates?

Yes. It works for any pair of dates on the Gregorian calendar, past or future. Enter the earlier date first for a positive count, or the later date first for a negative one.

Disclaimer: This calculator is for general information only. Day counts use the Gregorian calendar and the standard convention of excluding the start date; deadlines and legal dates are governed by the applicable contract, statute, or authority, which may count days differently.