Percentage Calculator
Three common percentage calculations in one place — instant results as you type.
What is X% of a number?
What % is X of Y?
Percentage change from X to Y
How percentages work
A percentage is a fraction of 100. The three most common percentage questions are: (1) find X% of a number, (2) find what share one number is of another, and (3) find the percentage change between two values.
Formulas
- X% of Y = Y × X ÷ 100
- A is what % of B = A ÷ B × 100
- % change = (new − old) ÷ old × 100
Frequently asked questions
What is 15% of 200?
15% of 200 = 200 × 15 ÷ 100 = 30.
How do I calculate percentage change?
Percentage change = (new − old) ÷ old × 100. Positive = increase, negative = decrease.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. E.g. 30 ÷ 200 × 100 = 15%.
Is my data sent anywhere?
No — all calculations run locally in your browser.
Percentages without the head-scratching
A percentage is just a fraction with 100 as the denominator: 18% means 18 out of every 100. Nearly every everyday percentage problem is one of three questions, and the calculator above answers all of them: what is X% of a number, what percentage one number is of another, and the percentage change from one value to another.
The three formulas are worth memorising. X% of N = N × X ÷ 100. A as a percentage of B = A ÷ B × 100. Change from A to B = (B − A) ÷ A × 100 — note the division is always by the starting value, which is where most mistakes happen.
Worked examples
Discount: a £79 pair of shoes at 35% off costs 79 × 0.65 = £51.35 — multiplying by (100 − 35)% in one step is faster than computing the discount and subtracting. Share: if 42 of 60 students passed, that is 42 ÷ 60 × 100 = 70%. Change: rent rising from £800 to £920 is (920 − 800) ÷ 800 × 100 = 15%, even though £120 “feels” like less.
The traps almost everyone falls into
- Percentage changes don’t cancel. A 20% drop followed by a 20% rise leaves you 4% down (0.8 × 1.2 = 0.96). The bigger the swing, the worse the asymmetry — a 50% loss needs a 100% gain to recover.
- Percentage points ≠ per cent. Interest moving from 2% to 3% is a rise of one percentage point but a 50% increase. News headlines mix these up constantly.
- Reverse percentages need division. If £120 is the price after 20% VAT, the net price is 120 ÷ 1.2 = £100, not 120 − 20% = £96.
- Stacked discounts multiply. 30% off then an extra 10% off is 0.7 × 0.9 = 37% off, not 40%.
Additional questions
How do I add VAT to a net price?
Multiply by 1.20 for 20% VAT (or 1.05 for the reduced 5% rate). To strip VAT out of a gross price, divide by the same factor — never subtract the percentage, because the VAT was calculated on the smaller net amount.
What is a “basis point”?
One hundredth of a percentage point, used where small rate moves matter: a mortgage rate rising 25 basis points went up 0.25 percentage points. It exists precisely to avoid the per cent vs percentage-point ambiguity.
Why does the order of percentage operations not matter?
Because percentage operations are multiplications, and multiplication is commutative: +10% then −15% gives 1.10 × 0.85 wherever you start. This also means you can check shop discounts in whichever order is easiest in your head.