Add Percentage Calculator
Add a percentage to a number — or take one off. Defaults to £80 plus 20% = £96; change the numbers to your own.
Adding a percentage means increasing a number by that share of itself: £80 plus 20% is £80 + £16 = £96. It is the «add X% to Y» sum behind price mark-ups, pay rises, deposits and adding VAT. Below: the formula, the working, and the mistakes people make with it.
How it works.
Formula: Y × (1 + X ÷ 100) to add X%; Y × (1 − X ÷ 100) to take X% off.
- Divide the percentage by 100 (20% becomes 0.20).
- Add it to 1 (1.20) — or subtract it from 1 (0.80) to take the percentage off.
- Multiply your number by that factor.
Worked example — £80 plus 20%: 20 ÷ 100 = 0.20; 1 + 0.20 = 1.20; 80 × 1.20 = £96.
Mental-maths shortcut. Find 10% (move the decimal one place left), scale it to the percentage you need, and add it on: 10% of 80 is 8, so 20% is 16, and 80 + 16 = 96.
Worked examples
£80 plus 20% = £96 — a £16 mark-up; the same sum as adding standard-rate VAT to an £80 net price.
£35,000 plus 5% = £36,750 — a 5% pay rise on a £35k salary (gross, before tax).
£250,000 plus 3% = £257,500 — a home worth 3% more after a year of house-price growth.
£1,928 plus 5.19% = £2,028 — an energy price cap rising by about 5%.
£120 minus 20% = £96 — the other direction: taking 20% off a £120 price.
Sources:
HMRC VAT rates
· retrieved 2026-08-30.
Frequently asked questions
How do I add a percentage to a number?
Multiply the number by (1 + percentage ÷ 100). £80 plus 20%: 80 × 1.20 = £96. Or work out the percentage first (20% of 80 = 16) and add it on (80 + 16 = 96) — same answer.
How do I add 20% to a price?
Multiply the price by 1.2. £50 × 1.2 = £60; £199 × 1.2 = £238.80. Adding 20% is exactly what adding UK standard-rate VAT does.
How do I add a percentage in Excel?
If the number is in A1 and the percentage in B1 as a plain number (20), use =A1*(1+B1/100). If B1 is formatted as a percentage (20%), use =A1*(1+B1).
Is adding 20% and then taking 20% off the same as where you started?
No. £100 plus 20% = £120; £120 minus 20% = £96, not £100. The second percentage is taken from a bigger number. To undo a 20% increase you divide by 1.2 rather than subtract 20% — see the reverse percentage calculator.
What is the difference between adding a percentage and a percentage increase?
Two views of the same change. Adding 20% to £80 gives £96; the percentage increase from £80 to £96 is 20%. Use this page when you know the starting number and the percentage; use the percentage increase calculator when you know both numbers and want the percentage.
How do I subtract a percentage from a number?
Multiply by (1 − percentage ÷ 100). £120 minus 20%: 120 × 0.80 = £96. Choose «Subtract» in the calculator above.