How to Calculate Tip: 15%, 18%, 20% Guide with Examples

The Short Answer

A tip is just a percentage of the bill. Convert the percentage to a decimal and multiply:

Tip = bill × (tip percentage ÷ 100)

A $48.50 dinner at 20%: 48.50 × 0.20 = $9.70 tip, for a $58.20 total. At 15%: 48.50 × 0.15 = $7.275 → $7.28. At 18%: 48.50 × 0.18 = $8.73.

Below you will find the formula worked out for every standard percentage, a mental-math shortcut that works in seconds, how to handle tax, how to split the bill fairly, tipping customs around the world, and the mistakes that cost people money.

The Basic Formula, Step by Step

Step 1 — Turn the percentage into a decimal. Divide by 100 (move the decimal point two places left): 20% → 0.20, 15% → 0.15, 18% → 0.18.

Step 2 — Multiply the bill by that decimal.

Step 3 — Round to the nearest cent (or nearest dollar if you like).

Step 4 — Add the tip to the bill for the total.

Worked Example: $64.80 bill

• 15%: 64.80 × 0.15 = 9.72 → tip $9.72, total $74.52 ✓
• 18%: 64.80 × 0.18 = 11.664 → tip $11.66, total $76.46 ✓
• 20%: 64.80 × 0.20 = 12.96 → tip $12.96, total $77.76 ✓

The Standard Percentages: 15%, 18%, 20%

In the United States, the customary restaurant tip is 15–20% of the pre-tax bill: 15% for adequate service, 18% for good service, and 20% (or more) for great service. Here is what each looks like on common bill sizes:

Check one: $48.50 × 0.15 = 7.275 → $7.28 ✓. $150 × 0.18 = $27.00 ✓. Every entry follows the same multiply-and-round rule.

The 10% Shortcut (Mental Math in Seconds)

The fastest way to tip without a calculator starts from 10% — just move the decimal point one place left:

• 10%: $64.80 → $6.48
• 20%: double the 10% → 2 × $6.48 = $12.96 ✓ (matches the formula above)
• 15%: 10% plus half of 10% → $6.48 + $3.24 = $9.72 ✓
• 18%: 20% minus 2% → $12.96 − $1.30 = $11.66 ✓ (2% of $64.80 = $1.296 ≈ $1.30)

Practice it once on a real receipt and it becomes automatic — no phone needed at the table.

Should You Tip on the Tax?

Etiquette says to tip on the pre-tax subtotal, not the after-tax total. The difference is small but real:

Take a $50.00 bill with 8% sales tax: tax = $4.00, total = $54.00.

• Tip on pre-tax: 50.00 × 0.20 = $10.00
• Tip on post-tax: 54.00 × 0.20 = $10.80

You save $0.80 by tipping on the subtotal. Servers will not notice or mind — pre-tax tipping is the standard expectation in the US. If the receipt only shows one total, tipping on the full amount is perfectly fine too; the difference is under a dollar on most meals.

Splitting the Bill Fairly

Two fair methods, depending on the group:

Method 1 — Split everything evenly. Add the tip to the bill, divide by the number of people. Example: $120.00 bill, 18% tip = $21.60, total $141.60, split 4 ways → $35.40 each ✓

Method 2 — Everyone covers their own. Each person tips on their own subtotal. Example: your share is $32.00, 20% tip = $6.40, you pay $38.40 ✓

Method 1 is simplest when everyone ordered similarly. Method 2 is fairer when one person had the steak and another had the salad — and it avoids the classic argument entirely.

Tipping Customs Around the World

Tipping is not universal, and the "right" percentage changes at the border:

• United States: 15–20% at restaurants; tip on pre-tax subtotal. Bartenders ~$1–2 per drink, delivery drivers 10–15%.
• United Kingdom & Ireland: 10–15% if no service charge is added; check the bill first — a 12.5% "discretionary service charge" is common in London.
• Continental Europe: rounding up or 5–10% is generous; service is usually included (service compris in France).
• Japan & South Korea: tipping can offend — good service is considered part of the job. Do not tip.
• Middle East: 10–15% is common where service is not included.
• Latin America: 10% is typical in restaurants in Mexico and Brazil; check whether servicio is already on the bill.

When in doubt, ask a local or check the receipt for an included service charge before adding more.

Common Mistakes to Avoid

Tipping on the total including tax. Standard practice is the pre-tax subtotal — see the worked example above.

Forgetting the tip when splitting. If four people split a $141.60 total-with-tip bill, each pays $35.40 — not $30.00. The tip is part of the total before you divide.

Double-tipping on an included gratuity. Large parties (often 6+) may have an automatic 18–20% gratuity printed on the bill. Read the receipt before adding another tip.

Tipping a percentage on a percentage. "Add 20% then add tax on top of that" is wrong ordering — tax applies to the food, tip applies to the subtotal; they are independent.

Rounding down aggressively. Rounding $9.72 to $9.00 to "keep it simple" quietly drops your tip from 15% to 13.9%. Round to the nearest dollar, or round up.

Quick Reference

Key Takeaways

• Tip = bill × (percentage ÷ 100) — 20% is × 0.20, 15% is × 0.15, 18% is × 0.18.
• The mental shortcut: find 10% (move the decimal), then double it for 20% or add half for 15%.
• Tip on the pre-tax subtotal, and check the receipt for an automatic gratuity before adding more.
• Split the total-with-tip evenly, or have each person tip on their own share.
• Customs vary: 15–20% in the US, ~10% in much of Europe and Latin America, and no tipping in Japan.