Field card · snappercentcalc.com
Percentage Cheat Sheet
Every percentage formula on one plate — worked examples, the shares worth memorising, and mental math shortcuts. Print it, pin it, done.
The four shares worth memorising
1%1/100 · 0.01
10%1/10 · 0.10
25%1/4 · 0.25
50%1/2 · 0.50
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
- 5%
- 1/20 · 0.05
- 12.5%
- 1/8 · 0.125
- 20%
- 1/5 · 0.20
- 33.3%
- 1/3 · 0.333
- 66.7%
- 2/3 · 0.667
- 75%
- 3/4 · 0.75
- 100%
- 1/1 · 1.00
- 150%
- 3/2 · 1.50
Mental math shortcuts
- 0110% = move the decimal one place left (10% of 340 = 34).
- 025% = half of 10% (5% of 340 = 17).
- 031% = move the decimal two places left (1% of 340 = 3.4).
- 04x% of y = y% of x (8% of 50 = 50% of 8 = 4).
- 0515% tip = 10% + half of that (10% of 60 = 6, +3 = 9).
- 06A 50% rise then a 50% fall leaves you 25% below the start.
- 07Doubling = +100%; halving = −50%.
- 08Rule of 72: 72 ÷ rate ≈ years to double.