ToolNestHow to Calculate Percentage
Percentages confuse people because there are really three different calculations hiding under one word. Here are all three — each takes ten seconds once you know the formula.
Case 1: What is X% of a number?
Formula: (X ÷ 100) × number. Example: 20% of 150 → (20 ÷ 100) × 150 = 0.2 × 150 = 30. This is the one you use for discounts, tips, and tax.
Case 2: What percent is X of Y?
Formula: (X ÷ Y) × 100. Example: 30 is what percent of 150? → (30 ÷ 150) × 100 = 0.2 × 100 = 20%. Use it for test scores, conversion rates, and progress tracking.
Case 3: Percent increase or decrease
Formula: ((new − old) ÷ old) × 100. Example: price rose from $50 to $65 → ((65 − 50) ÷ 50) × 100 = 30% increase. A drop from $50 to $40 is a 20% decrease.
The one-line shortcut
To find X% of a number, just move the decimal two places left on X and multiply: 15% of 200 → 0.15 × 200 = 30. For 10%, move one place: 10% of 200 = 20.
Common traps
'Increase by 200%' means triple, not double (100% + 200% = 300%). And 50% off followed by 50% off is 75% off total, not free — percentages compound on the new base.
Do it instantly
Our free tip & percentage calculator handles bills, tips, and splits — showing every step of the math.