Percentage Calculator
Three percentage operations in one tool: find X% of a number, work out what percent A is of B, and calculate the percentage change between two values.
How it works
Percent of a number: number × percent ÷ 100. So 18% of £850 is 850 × 18 ÷ 100 = £153.
What percent A is of B: A ÷ B × 100. £45 out of £180 is 45 ÷ 180 × 100 = 25%.
Percentage change: (new − old) ÷ old × 100. A price rising from £2,000 to £2,500 is a 25% increase; the same formula gives a negative result for decreases. Always divide by the ORIGINAL value — dividing by the new one is the classic mistake.
FAQ
How do I work out a percentage of a number?
Multiply the number by the percentage and divide by 100: 18% of 850 is 850 × 18 ÷ 100 = 153. Mental shortcut: find 10% by dividing by ten, 1% by dividing by a hundred, then scale up — the fastest way to sanity-check discounts and tips.
How do I calculate percentage increase or decrease?
Subtract the old value from the new, divide by the old value, multiply by 100: (new − old) ÷ old × 100. Rent going from £1,200 to £1,320 is a 10% increase. The base is always the original figure; using the new figure understates rises and overstates falls.
How do stacked discounts combine?
They multiply rather than add: 20% off then a further 10% off leaves you paying 0.80 × 0.90 = 72% — a 28% total discount, not 30%. The same logic applies to consecutive price rises, which is why two 10% increases add up to 21%, not 20%.