Calculating a tip in your head is a skill that pays for itself. Below are the fast mental-math tricks for 15%, 18%, 20%, and 25% tips — plus a free tip calculator that splits the bill between any number of people.
A tip is just a percentage of the bill. If you know how to find 10% of a number, you can derive almost any common tip percentage from it in your head — because 15%, 20%, and 25% are all simple multiples or fractions of 10%.
To find 10% of any number, move the decimal point one place to the left. So:
Every other common tip percentage is built on that foundation.
Find 10%, then add half of it. On a $60 bill: 10% is $6.00, half of that is $3.00, so 15% is $9.00.
Find 10%, then double the 10% and multiply by 0.8 (or just add 80% of the 10% value). In practice: find 20%, then subtract a tenth of that. On a $50 bill: 20% is $10.00, a tenth of that is $1.00, so 18% is $9.00.
Find 10%, then double it. On a $45 bill: 10% is $4.50, so 20% is $9.00. This is the fastest tip to calculate mentally, which is one reason it's so popular.
Find 10%, then multiply by 2.5 — or find 20% and add half of the 10% value. On a $40 bill: 20% is $8.00, half of 10% is $2.00, so 25% is $10.00.
Here's what each common tip looks like on a few sample bills. Once you internalize a few, the mental math becomes automatic.
| Bill | 15% | 18% | 20% | 25% |
|---|---|---|---|---|
| $20 | $3.00 | $3.60 | $4.00 | $5.00 |
| $40 | $6.00 | $7.20 | $8.00 | $10.00 |
| $60 | $9.00 | $10.80 | $12.00 | $15.00 |
| $80 | $12.00 | $14.40 | $16.00 | $20.00 |
| $100 | $15.00 | $18.00 | $20.00 | $25.00 |
| $150 | $22.50 | $27.00 | $30.00 | $37.50 |
In the United States, tipping customs for table service at a sit-down restaurant typically fall into these ranges:
For other service contexts, standards vary widely:
Outside the US, tipping norms differ significantly. In much of Europe, a small tip or rounding up is typical because service is included in the price. In Japan, tipping is often considered rude. In many parts of Asia, Africa, and Latin America, tipping expectations vary from optional to expected depending on the country. It's worth checking local customs before you travel.
Etiquette guides generally recommend tipping on the pre-tax subtotal, since sales tax isn't part of the service you received. That said, most people tip on the total for simplicity, and the difference is usually small — a few cents on a typical bill. Either approach is considered acceptable.
If you want to be precise, look for the subtotal line above the tax line on your receipt and calculate from there.
When multiple people are paying, the safest approach is to add the tip to the bill first, then divide. This avoids the rounding errors that creep in when you split first and tip separately.
Example: four people share a $160 bill and want to leave a 20% tip. Add 20% ($32) to get a total of $192. Divide by four: $48 per person.
If you split first ($40 each) and then calculate the tip on that, you may end up a few cents short if everyone rounds down. Adding the tip first solves that.
For simplicity, many people round the total to the nearest dollar or the nearest convenient number. If the bill is $47.30 and you want to leave a 20% tip ($9.46), rounding the total to $57 makes for a clean tip of $9.70 — close enough, and much easier than counting coins.
Rounding up is always in the server's favor, and it's a nice gesture when the service was good.
If you'd rather not do mental math — or you're splitting the bill among several people and want exact per-person totals — the free tip calculator handles all of it:
It works in any browser, offline, and requires no account.