💡 How-To
How to Calculate Tip in Your Head (15%, 18%, 20%)
Tipping at restaurants is mandatory in the US (15-20%), but most people pull out their phone to calculate it. These mental math tricks make it instant.
Quick Tip Reference
| Bill | 15% | 18% | 20% |
|---|---|---|---|
| $20 | $3.00 | $3.60 | $4.00 |
| $35 | $5.25 | $6.30 | $7.00 |
| $50 | $7.50 | $9.00 | $10.00 |
| $75 | $11.25 | $13.50 | $15.00 |
| $100 | $15.00 | $18.00 | $20.00 |
Mental Math Tricks
10% Trick (The Foundation)
- Just move the decimal point left one place
- $45.00 → $4.50 (10%)
- $82.50 → $8.25 (10%)
- This is the basis for all other tip calculations
20% = Double the 10%
- $45.00 → $4.50 (10%) → $9.00 (20%)
- $82.50 → $8.25 (10%) → $16.50 (20%)
- Just double the 10% amount
15% = Half the 20% + the 10%
- $45.00: 10% = $4.50, 20% = $9.00, so 15% = $6.75
- Or: 10% + half of 10% = $4.50 + $2.25 = $6.75
18% = 20% minus 2%
- $45.00: 20% = $9.00, 2% = $0.90, so 18% = $8.10
- Or: 10% + 8% (just under the 10%)
The "Move the Decimal" Method
- Step 1: Move the decimal point one place left = 10%
- Step 2: For 20%, double that number
- Step 3: For 15%, take 10% + half of 10%
- Step 4: For 18%, take 20% and subtract 2% (one-fifth of the 10%)
The split-the-bill trick: When splitting with friends, calculate the tip first, then divide. Example: $80 bill for 4 people. 20% tip = $16. Total = $96. Each person pays $24. This is easier than dividing first and then adding tip per person.
⚠️ Tipping rules in the US:
- Full-service restaurant: 15-20% of pre-tax bill
- Counter service (coffee, fast casual): 10-15% or $1-2
- Delivery: 15-20% or $5 minimum
- Bars: $1 per drink or 15-20% of tab
- Tipping is not optional in the US " — servers earn $2-3/hour base pay
The bottom line: The fastest mental math: move the decimal left for 10%, double it for 20%. For 15%, take the 10% and add half of itself. For 18%, take the 20% and subtract 2% (one-fifth of the 10%). Practice once or twice and it becomes automatic.