How to Calculate a Tip
To calculate a tip, multiply the bill by the tip percentage and divide by 100, then add the tip to the bill to get the total. On an $85.00 bill at 20%, the tip is $85.00 times 20 divided by 100, which is $17.00, and the total is $102.00. The free tip calculator above does this instantly, but the mental tricks on this page let you do it at the table without one.
The formula is one line, and the tricks are all built on the same idea: 10% of any bill is the bill with the decimal point moved one place to the left. From 10% you can reach 15%, 18%, 20% and 25% with one more small step. This page works through the formula, the four tricks, and worked examples on $46, $85, $120 and $200 bills, so you can calculate any tip in a few seconds.
The Tip Formula
The tip formula is: tip equals the bill times the tip percentage divided by 100. The total equals the bill plus the tip. The per-person share equals the total divided by the number of people. Written out for the default bill: tip equals $85.00 times 20 divided by 100, which is $17.00; total equals $85.00 plus $17.00, which is $102.00; per person for two people equals $102.00 divided by 2, which is $51.00.
The formula works for any percentage. For 15% on $85.00, the tip is $85.00 times 15 divided by 100, which is $12.75. For 18%, it is $85.00 times 18 divided by 100, which is $15.30. For 25%, it is $85.00 times 25 divided by 100, which is $21.25. The calculator above applies the same formula, with the added steps of sales tax, splitting, and round-up.
Step 1 — Write down the bill
Use the subtotal before tax. On the examples below the bills are $46.00, $85.00, $120.00 and $200.00, all pre-tax. Write the bill down or hold it in your head — the tricks need only the bill and the percentage.
Step 2 — Find 10% by moving the decimal
Move the decimal point one place to the left. Ten percent of $85.00 is $8.50, ten percent of $46.00 is $4.60, ten percent of $120.00 is $12.00, and ten percent of $200.00 is $20.00. This one move is the foundation of every trick below.
Step 3 — Build the percentage you want from 10%
Double 10% to get 20%, add half of 10% to get 15%, subtract 2% from 20% to get 18%, and divide the bill by four to get 25%. Each trick is one small step from the 10% figure, and each is shown with numbers in the next section.
Worked Examples: Calculating Tips by Hand
Each row shows a bill and the tip at the four percentages people use most, with the mental trick that gives each figure. All figures come from the calculator above.
| Bill | 10% (move decimal) | 15% (10% + half) | 20% (10% doubled) | 25% (bill / 4) |
|---|---|---|---|---|
| $46.00 | $4.60 | $6.90 | $9.20 | $11.50 |
| $85.00 | $8.50 | $12.75 | $17.00 | $21.25 |
| $120.00 | $12.00 | $18.00 | $24.00 | $30.00 |
| $200.00 | $20.00 | $30.00 | $40.00 | $50.00 |
Check the 15% column: on $85.00, 10% is $8.50, half of that is $4.25, and $8.50 plus $4.25 is $12.75. On $120.00, 10% is $12.00, half is $6.00, and the sum is $18.00. Check the 25% column: $85.00 divided by 4 is $21.25, and $200.00 divided by 4 is $50.00. The 18% figure needs one more step: 20% minus 2%, where 2% is one-fifth of 10%. On $85.00, 20% is $17.00 and 2% is $1.70, so 18% is $15.30.
How to Use the Tip Calculator
The calculator is the check on your mental maths. Enter the bill, tap a preset, and compare the result with the figure you worked out in your head.
- Enter the bill. Type the subtotal printed on the check, before tax.
- Tap a preset. The 10%, 15%, 18%, 20% and 25% buttons apply the percentage instantly.
- Compare with your mental figure. If your hand calculation says $17.00 and the calculator says $17.00, both are right.
- Try a custom percentage. Type any percentage, such as 22%, and the calculator applies the same formula.
- Split the bill. Enter the number of people and the calculator divides the total evenly.
The comparison table under the result is the fastest check of all: it shows 15%, 18%, 20% and 25% on your bill at once. On the $85.00 default bill, the four tips are $12.75, $15.30, $17.00 and $21.25, with totals of $97.75, $100.30, $102.00 and $106.25.
The Four Mental Tricks in Detail
Each trick is one step from the 10% figure, and each works on any bill. Learn them in order, and the 20% trick first — it is the one you will use most.
| Trick | How it works | On $85.00 | On $120.00 |
|---|---|---|---|
| 10% | Move the decimal one place left | $8.50 | $12.00 |
| 15% | 10% plus half of 10% | $12.75 | $18.00 |
| 18% | 20% minus 2% (2% is one-fifth of 10%) | $15.30 | $21.60 |
| 20% | 10% doubled | $17.00 | $24.00 |
| 25% | Divide the bill by four | $21.25 | $30.00 |
The 18% trick is the only one with two steps: first find 20% by doubling 10%, then find 2% by dividing 10% by five, then subtract. On $120.00, 20% is $24.00, 2% is $2.40, and 18% is $21.60. With practice the whole chain takes a few seconds, and the calculator above is there whenever you want to check.
Common Mistakes When Calculating a Tip
Mental maths has a few classic slips. They are easy to spot once you know them.
- Moving the decimal the wrong way. Ten percent of $85.00 is $8.50, not $0.85 and not $85.00. One place left, no more.
- Adding the tip to the wrong total. The total is the bill plus the tip: $85.00 plus $17.00 is $102.00, not $85.00 plus $20.00.
- Forgetting to split the tip. The per-person share includes the tip: two people on a $102.00 total pay $51.00 each, not $42.50 each plus a forgotten tip.
- Calculating the tip on the post-tax total by accident. On an $85.00 bill with 8% tax, the post-tax 20% tip is $18.36, not $17.00. Use the subtotal unless you mean to tip on the total.
- Rounding down. Rounding $16.80 down to $16.00 saves $0.80 and costs the server the same. Round up, not down.
- Doubling the wrong number for 20%. Twenty percent is double 10%, which is $8.50 doubled to $17.00 — not double the bill, and not double 15%.
Where Mental Tip Maths Helps
A calculator is always better for exact figures, but mental maths covers the moments when you do not have one to hand.
- At the table. The bill arrives, the card machine is coming, and you want the number before it appears.
- Delivery at the door. Cash in hand, a quick 20% in your head, and the driver is paid without a pause.
- Splitting with friends. A fast per-person figure settles the split before anyone opens a phone.
- Checking the terminal. Knowing the right tip lets you spot when a terminal suggests a post-tax figure.
- Small bills. On a $12.00 coffee tab, 20% is $2.40 — faster in your head than in an app.
Tips for Accurate Results
Five habits keep hand calculations right.
- Start from 10% every time. It is the anchor for every other percentage, and it is one decimal move.
- Say the numbers out loud. “Ten percent is eight-fifty, double it is seventeen” is harder to get wrong than silent arithmetic.
- Check against the calculator. Enter the same bill above and compare the result with your mental figure.
- Round the bill first for a rough check. On an $86.40 bill, round to $85.00, work out 20% as $17.00, and treat the exact figure as a small step up.
- Split last, not first. Calculate the tip on the whole bill, then divide the total. Splitting first and tipping each share gives the same answer, but the whole-bill way is simpler.
Tip Calculation Quick Answers
The figures people look up most often when calculating a tip by hand.
| Question | Answer |
|---|---|
| 20% of $85.00 | $17.00, total $102.00 |
| 15% of $85.00 | $12.75, total $97.75 |
| 18% of $85.00 | $15.30, total $100.30 |
| 20% of $46.00 | $9.20, total $55.20 |
| 20% of $200.00 | $40.00, total $240.00 |
Related tools on this site: the main tip calculator, the percentage calculator for the same formula on any numbers, and the discount calculator for sale prices. For the US norms behind the percentages, the NerdWallet tip calculator guide explains the pre-tax convention and the usual rates.
Frequently Asked Questions
How do you calculate a 20% tip?
Move the decimal one place left to get 10% of the bill, then double it. On an $85.00 bill, 10% is $8.50, so 20% is $17.00, and the total is $102.00.
How do you calculate a 15% tip?
Find 10% by moving the decimal, then add half of that number. On an $85.00 bill, 10% is $8.50, half is $4.25, and the sum is $12.75.
What is 18% of $85?
Eighteen percent of $85.00 is $15.30. The quick way is 20% minus 2%: 20% is $17.00 and 2% is $1.70, so 18% is $15.30.
How do you calculate a tip for a group?
Calculate the tip on the whole bill first, add it to the bill, then divide the total by the number of people. On an $85.00 bill at 20%, two people pay $51.00 each, three pay $34.00 each, and four pay $25.50 each.
Do you calculate the tip before or after tax?
Before tax is the US convention: calculate the tip on the pre-tax subtotal. On an $85.00 bill with 8% tax, the pre-tax 20% tip is $17.00 and the post-tax tip is $18.36.
Disclaimer: This guide is for general information only. Tipping norms vary by region and establishment; the amounts shown are estimates, not legal or financial advice. Always check your bill for service charges before adding a tip.