The Tip Formula
The math behind every tip is the same simple formula:
Example: $65 bill × (20 ÷ 100) = $65 × 0.20 = $13.00 tip
That's it. Everything below is just different ways to make this calculation faster and easier — whether you're doing it mentally or on paper.
Method 1: The Decimal Shift (Best for Mental Math)
This is the fastest way to calculate a 20% tip in your head and it works for any bill amount.
How it works:
1. Move the decimal one place to the left → that's 10%
2. Double it → that's 20%
3. Or add half → that's 15%
Worked examples:
| Bill | ÷10 = 10% | ×2 = 20% tip | +half = 15% tip |
|---|---|---|---|
| $40.00 | $4.00 | $8.00 | $6.00 |
| $55.00 | $5.50 | $11.00 | $8.25 |
| $72.00 | $7.20 | $14.40 | $10.80 |
| $93.50 | $9.35 | $18.70 | $14.03 |
| $120.00 | $12.00 | $24.00 | $18.00 |
Method 2: The Tax Doubling Trick (Quick 18–20%)
This trick only works in states where sales tax is around 8–10%, but it's very fast.
How it works:
Find the tax amount on your bill, then double it. In most US states, doubling the tax gives you roughly 18–20% of the pre-tax bill.
Double the tax: $4.80 × 2 = $9.60 tip ≈ 16% tip
This is fast and good enough when you're just trying to get in the right ballpark without a calculator.
Method 3: Multiply by the Decimal (Most Accurate)
When you have a phone calculator handy, this is the most precise approach for any percentage.
How it works:
Convert the tip % to a decimal by dividing by 100:
15% = 0.15 | 18% = 0.18 | 20% = 0.20 | 25% = 0.25
Then: Bill × decimal = tip
$85.00 × 0.20 = $17.00 (20% tip)
$85.00 × 0.25 = $21.25 (25% tip)
How to Calculate the Total Bill with Tip
Once you have the tip, adding it to get the total is simple:
Or: Total = Bill × (1 + tip decimal)
Example: $65 bill with 20% tip → $65 × 1.20 = $78.00 total
How to Split a Tip
When splitting a bill between multiple people:
Example: $18 tip ÷ 3 people = $6.00 per person
Or just use our split bill calculator to handle the whole thing in one step.
Quick Tip Reference — Common Bill Amounts
| Bill | 15% Tip | 18% Tip | 20% Tip | 25% Tip |
|---|---|---|---|---|
| $25 | $3.75 | $4.50 | $5.00 | $6.25 |
| $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 |
| $200 | $30.00 | $36.00 | $40.00 | $50.00 |
Frequently Asked Questions
What is the easiest way to calculate 20% tip?
The easiest mental method: move the decimal one place left (10%), then double it. On $74 → $7.40 → $14.80 tip. Or just use our free calculator above for instant results on any amount.
How do you calculate an 18% tip?
Find 10% (move decimal), then find 8% (multiply 10% by 0.8), and add them: 10% + 8% = 18%. Or multiply the bill by 0.18. On $50: $5.00 + $4.00 = $9.00 tip.
Should I calculate the tip on pre-tax or post-tax?
Traditionally, tips are calculated on the pre-tax subtotal. However, tipping on the full total is common and the difference is usually only $1–3 on a typical dinner. Either approach is acceptable.
How do I calculate a tip with a phone calculator?
Type your bill amount, tap multiply (×), type your tip as a decimal (0.15 for 15%, 0.20 for 20%), then press equals. That's your tip amount. Add it to the original bill for the total.