The basic tip formula
A tip is a percentage of the bill amount you choose as the base. Convert the tip rate to a decimal and multiply. Then add the tip to the bill for the total.
Total = bill + tip
A calculator gives an exact result, but a few simple relationships make the most common rates easy to estimate in your head.
Fast mental shortcuts
10% tip
Move the decimal one place left. $46 becomes $4.60.
20% tip
Find 10%, then double it. $4.60 becomes $9.20.
15% tip
Add 10% and half of 10%. $4.60 + $2.30 = $6.90.
25% tip
Divide by four. One quarter of $46 is $11.50.
Worked example: 20% on a $46 bill
Ten percent of $46 is $4.60. Double that for 20%.
Total: $46 + $9.20 = $55.20
Answer: a 20% tip is $9.20.
How to find 15% quickly
Fifteen percent is 10% plus 5%. The 5% amount is half of the 10% amount. This approach avoids multiplying by 0.15 directly.
Worked example: 15% on a $72 bill
5% of $72 = $3.60
15% tip = $7.20 + $3.60 = $10.80
Total = $82.80
Answer: a 15% tip is $10.80.
How to find 18%
Eighteen percent is 20% minus 2%. Find 20% by doubling 10%. Find 2% by dividing the 10% amount by five, then subtract.
Worked example: 18% on a $65 bill
20% = $13.00
2% = $6.50 ÷ 5 = $1.30
18% tip = $13.00 − $1.30 = $11.70
Answer: an 18% tip is $11.70, making the total $76.70.
Round first for a fast estimate
When you need speed more than exact cents, round the bill to a nearby easy number, estimate the tip, then adjust if necessary. A $58.70 bill rounds to $60. Twenty percent of $60 is $12, so a 20% tip on the exact amount will be just under $12. The exact tip is $11.74.
Rounding up can also make both the arithmetic and the final payment simpler. The amount you choose to leave remains your decision.
How to split a bill with tip
For an even split, calculate the tip, add it to the bill, and divide the final total by the number of people.
Worked example: $84 bill, 20% tip, split three ways
Total: $84 + $16.80 = $100.80
Each: $100.80 ÷ 3 = $33.60
Answer: each person pays $33.60.
An equal split makes sense when everyone agrees to it. If orders were very different, calculate each person’s food and drink share first, then apply the same tip rate to each subtotal. Confirm that the individual shares add back to the full bill and tip.
Tip before tax or after tax?
Using the pre-tax subtotal means the tip is based only on the listed goods or service. Using the final total means tax is included in the base and produces a slightly larger tip. Customs vary by place and situation, so the key mathematical step is to identify which number you are using.
Worked comparison: $80 subtotal, $6.40 tax, 20% tip
On after-tax total: $86.40 × 0.20 = $17.28
The difference is $1.28. Either calculation can be done correctly once the base is stated.
Common mistakes to avoid
Moving the decimal the wrong direction: 10% of $50 is $5, not $50 or 50 cents. Dividing before adding the tip: for an even split, use the complete total. Adding a tip twice: check whether a service charge or gratuity already appears on the bill. Forgetting the base: decide whether your chosen rate applies to the pre-tax subtotal or the final amount.
Try it: use the free tip & bill split calculator for instant results.