Percentage Calculator
Three calculators in one: find X% of a number, work out what one number is as a percentage of another, and calculate the percentage increase or decrease between two values.
Percentage calculator
Pick a mode and enter your numbers.
Runs entirely in your browser. Nothing you enter is saved or sent anywhere.
The three most common percentage sums
Most percentage questions come down to one of three forms: finding a percentage of a number, expressing one number as a percentage of another, or measuring the percentage change from an old value to a new one. This tool covers all three so you never have to remember which formula goes where.
X% of Y = (X ÷ 100) × Y. A as a % of B = (A ÷ B) × 100. % change = ((new − old) ÷ old) × 100. So 20% of 250 is 50; 30 is 25% of 120; and 80 → 100 is a 25% increase.
Percentage formulas at a glance
| Question | Formula |
|---|---|
| X% of Y | (X ÷ 100) × Y |
| A is what % of B | (A ÷ B) × 100 |
| % increase / decrease | ((new − old) ÷ old) × 100 |
| Reverse a percentage | part ÷ (percent ÷ 100) |
Percentage change vs percentage points
A common trap is mixing up percentage change with percentage points. If an interest rate rises from 5% to 7%, that is a 2 percentage-point rise, but a 40% increase in the rate. Both are correct — they answer different questions. Percentages run through a lot of everyday money decisions, from a council tax discount to the change in prices over time.
Frequently asked questions
How do I work out a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 20% of 250 is (20 ÷ 100) × 250 = 50. The first mode of this calculator does it for you.
How do I find what percentage one number is of another?
Divide the first number by the second and multiply by 100. For example, 30 out of 120 is (30 ÷ 120) × 100 = 25%. Use the second mode for this.
How do I calculate a percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100. Going from 80 to 100 is ((100 − 80) ÷ 80) × 100 = 25% increase. The third mode handles increases and decreases.
What is the difference between percentage change and percentage points?
Percentage change is relative to the starting value. Percentage points are the simple difference between two percentages — going from 5% to 7% is a 2 percentage-point rise but a 40% increase.
Can it reverse a percentage?
Yes. Knowing a value as a percentage of another lets you reverse it: if £60 is 20% of a total, the total is £60 ÷ 0.20 = £300. The 'what % of' and 'change' modes cover the common reverse cases.