About percentage calculations
Percentages show up everywhere — discounts, marks, tax, tips, interest, statistics — and they come in three distinct flavors that are easy to mix up. This calculator handles each one separately and shows the working, so you get the number and the method.
The three problems it solves
- What is X% of Y? — a 15% tip on 200 is (15 ÷ 100) × 200 = 30. Use it for discounts, VAT and commissions.
- X is what percent of Y? — scoring 30 out of 200 is (30 ÷ 200) × 100 = 15%. Use it for marks, progress and shares of a total.
- Percentage change — a price rising 250 → 300 is (300 − 250) ÷ 250 × 100 = a 20% increase. Use it for growth, inflation and salary changes.
Quick mental math tricks
- 10% is one decimal shift (10% of 350 = 35); 5% is half of that; 1% is two shifts.
- X% of Y always equals Y% of X — 8% of 50 feels hard, 50% of 8 is obviously 4.
- A 20% rise then a 20% fall does not return to the start: 100 → 120 → 96, because the fall applies to the bigger number.
- Percentage points differ from percent: going from 10% to 15% is +5 points, but a 50% relative increase.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply: 15% of 200 is (15 ÷ 100) × 200 = 30. The first calculator does this and shows the working.
What's the difference between percentage change and percentage points?
Going from 10% to 15% is a rise of 5 percentage points, but a 50% relative increase. News about interest rates and polls mixes these up constantly — the third calculator computes true percentage change.
Why can't the old value be zero in percentage change?
Percentage change divides by the old value, and dividing by zero is undefined — there's no meaningful percentage to describe going from 0 to something.