Percentage Cheat Sheet
Every percentage formula you need on one page — with worked examples, a fraction conversion table and mental math shortcuts. Print it, pin it, done.
The 12 core formulas
| Calculation | Formula | Example |
|---|---|---|
| Percentage of a number | Part = (P ÷ 100) × Whole | 25% of 200 = 50 |
| What percent is X of Y | P = (X ÷ Y) × 100 | 30 of 150 = 20% |
| Percentage increase | ((New − Old) ÷ Old) × 100 | 50 → 65 = +30% |
| Percentage decrease | ((Old − New) ÷ Old) × 100 | 80 → 60 = −25% |
| Percentage difference | |A − B| ÷ ((A + B) ÷ 2) × 100 | 40 vs 60 = 40% |
| Discount price | Price × (1 − D ÷ 100) | 20% off $80 = $64 |
| Reverse percentage | Original = Final ÷ (1 − D ÷ 100) | $64 after 20% off = $80 |
| Add VAT / tax | Net × (1 + R ÷ 100) | $100 + 20% VAT = $120 |
| Remove VAT / tax | Gross ÷ (1 + R ÷ 100) | $120 incl. 20% = $100 |
| Markup on cost | ((Price − Cost) ÷ Cost) × 100 | $40 → $50 = 25% markup |
| Profit margin | ((Price − Cost) ÷ Price) × 100 | $40 → $50 = 20% margin |
| Tip amount | Bill × (T ÷ 100) | 18% of $60 = $10.80 |
Percent, fraction and decimal
1%1/1000.01
5%1/200.05
10%1/100.10
12.5%1/80.125
20%1/50.20
25%1/40.25
33.3%1/30.333
50%1/20.50
66.7%2/30.667
75%3/40.75
100%1/11.00
150%3/21.50
Mental math shortcuts
- 10% = move the decimal one place left (10% of 340 = 34).
- 5% = half of 10% (5% of 340 = 17).
- 1% = move the decimal two places left (1% of 340 = 3.4).
- x% of y = y% of x (8% of 50 = 50% of 8 = 4).
- 15% tip = 10% + half of that (10% of 60 = 6, +3 = 9).
- A 50% rise then a 50% fall leaves you 25% below the start.
- Doubling = +100%; halving = −50%.
- Rule of 72: 72 ÷ rate ≈ years to double.