Percentage Calculator
Work out a percentage of a number, or undo a rise or a discount with the reverse percentage calculator. Pick a mode and type two numbers.
The calculator never sends or saves what you type.
On this page
X is what percent of Y?
This opens the marks-style part-of-a-whole tool with your numbers — its fields read "Marks obtained" and "Total marks", and the arithmetic, part ÷ whole × 100, is the same for any part and any whole.
Looking for a specific case?
- From one number to another — the rise or fall between two values, as a signed percentage. Percentage change calculator.
- Back to the value before a change — the multiplier method, the common mistake and the exam-style practice. Reverse percentage calculator · GCSE questions.
- VAT inside a price — the net amount and the VAT portion from a gross total, or VAT added to a net price. Reverse VAT calculator.
- A percentage off — what you pay and what you save at any discount. Discount calculator.
- Marks and CGPA — a score out of a total as a percentage, or a CGPA converted at your board's factor. Marks percentage calculator · CGPA to percentage.
- GPA from letter grades — unweighted and weighted, with honors and AP credit. High school GPA calculator.
- Wins, losses and ties — a record as a win percentage and the .xxx standings figure, with ties as half a win or left out. Win percentage calculator.
- Body weight — weight lost as a percentage of your starting weight, with 5% and 10% milestones and a goal weight. Weight loss percentage calculator.
How to calculate a percentage
The calculator above answers three kinds of percentage question: find a part of a number, change a number by a percentage, or go back to the number a change started from. Here is each one by hand.
1 · A percentage of a number
Multiply by the percentage, divide by 100
15% of 240: 240 × 15 ÷ 100 = 36. Or turn the percentage into a decimal first — 15% is 0.15 — and multiply once: 240 × 0.15 = 36. The unitary route finds 1% and scales it: 1% of 240 is 2.40, so 15% is 2.40 × 15 = 36. Try 15% of 240.
2 · Increase or decrease by a percentage
Find the part, then add it or take it away
80 raised by 20%: 20% of 80 is 16, so 80 + 16 = 96; lowered by 20% it is 80 − 16 = 64. In one step, multiply by 1 + 0.2 = 1.2 to add and by 1 − 0.2 = 0.8 to subtract. The "% of a number" mode prints both results under the part. Try 20% of 80.
3 · The value before a change
Divide by the multiplier — never add the percentage back
A jacket is £51 after 15% off. 85% of the original is left, so the original was 51 ÷ 0.85 = £60 — not 51 + 15%, which gives £58.65 and is wrong. After a rise, divide by 1 plus the rate: £132 after a 10% rise was 132 ÷ 1.1 = £120. Try £51 after 15% off · Try £132 after a 10% rise.
The percentage formula
Part = Whole × Percentage ÷ 100
One formula, three unknowns. Solve it for whichever you are missing:
- Percentage = Part ÷ Whole × 100 — "36 is what percent of 240?" → 15%
- Whole = Part ÷ Percentage × 100 — "36 is 15% of what?" → 240
The second line is the X is Y% of what number question, which has its own page with the unitary method worked through.
The reverse question uses the same rearrangement: when the part you know is the value after a change, the "whole" is the original, and the percentage you divide by is 100 plus or minus the change — which is the division in example 3 above.
Percentage change between two numbers
When you have a starting value and a finishing value and want the change as a percentage, the base is always the starting value: subtract it from the finishing value, divide by it, multiply by 100. From 40 to 50 is (50 − 40) ÷ 40 × 100 = +25%; from 50 back to 40 is (40 − 50) ÷ 50 × 100 = −20%, not −25%, because the base changed. The percentage change calculator takes the two values directly and keeps the sign.
Reverse percentages
A reverse percentage runs the arithmetic backwards: you know the value after a discount, a VAT charge or a pay rise, and you want the value before it. The "after a decrease" and "after an increase" modes above do it; the reverse percentage calculator is the full page — the multiplier table, three methods, the GCSE practice and the awkward cases.
The mistake almost everyone makes is explained on the reverse percentage calculator →
Frequently asked questions
How do I work out a percentage on a calculator?
Turn the percentage into a decimal by dividing it by 100, then multiply. For 15% of 240, key in 240 × 0.15 and you get 36. On a calculator with a % key, 240 × 15 % gives the same 36. To find what percentage one number is of another, divide the part by the whole and multiply by 100: 36 ÷ 240 × 100 = 15.
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. 15% of 240 is 240 × 15 ÷ 100 = 36. Finding 1% first works too: 1% of 240 is 2.40, so 15% is 2.40 × 15 = 36. The calculator above prints both routes under Show steps.
How do I add or take off a percentage?
Multiply by 1 plus or minus the percentage as a decimal. Adding 20% to 80 is 80 × 1.2 = 96; taking 20% off 80 is 80 × 0.8 = 64. The calculator above prints both results under the answer in "% of" mode. If you have two numbers and want the percentage between them, that is a percentage change, which has its own calculator.
What does percent mean?
Percent means "per hundred", from the Latin per centum. 15 percent is 15 out of every 100 — the fraction 15/100, or the decimal 0.15. That is why every percentage calculation is a multiplication or division by 100: a percentage is just a fraction whose denominator is always 100.
All calculators
Percentage Guru is a growing family of percentage tools — every one of them is below.
Reverse percentages
Prices, discounts & tips
Increase, decrease & change
Marks, grades & GPA
Every calculator with a one-line description of when to use it: All calculators and guides.