Summary: how to calculate a percentage for free and privately
A percentage calculator turns a question such as “what is 15% of 80?” into an answer and shows how it was reached. Pick one of the seven question types, type two numbers, and the Solution panel shows the answer, the step-by-step working and the formula applied.
The basic rule is percentage ÷ 100 × number, so 15% of 80 is 15 ÷ 100 × 80 = 12. The other modes rearrange the same idea. Nothing is uploaded: the arithmetic runs in your browser, and you can confirm that in the Network tab of your browser DevTools.
Table of use: questions, modes and answers
| Question | Mode | Enter | Answer |
|---|---|---|---|
| How much do I save with 20% off 80? | What is X% of Y? | Percentage 20, Number 80 | 16 |
| I scored 45 out of 60. What percent is that? | X is what % of Y? | Part 45, Whole 60 | 75% |
| 30 is 15% of what number? | X is Y% of what? | Part 30, Percentage 15 | 200 |
| Pay rose from 50,000 to 55,000. | Percentage change from X to Y | Original 50000, New 55000 | +10% |
| How far apart are two quotes, 80 and 100? | Percentage difference between X and Y | First 80, Second 100 | 22.222222% |
| What is 250 with 18% tax added? | Increase X by Y% | Number 250, Increase by 18 | 295 |
Percentage change is (new − old) ÷ old × 100. Percentage difference is |A − B| ÷ ((|A| + |B|) ÷ 2) × 100. Adding P percent multiplies by (1 + P ÷ 100) and taking it off multiplies by (1 − P ÷ 100).
Features
- Seven question types switched with a button, with the input labels changing to match (Part and Whole, Original Value and New Value, and so on).
- Working shown. The Solution panel lists a Step-by-Step Solution and a Formula Applied line using your own numbers.
- Direction at a glance. A percentage change shows a plus sign and green for an increase, red for a decrease.
- Negative numbers and decimals. A negative original value is divided by its absolute value, so going from −50 to −25 reads as a 50% rise.
- Honest rounding. Answers show up to 6 decimal places, steps up to 10, and a ≈ sign and a rounding note appear whenever a value was rounded.
- Clear errors instead of nonsense when a whole, a percentage or an original value of 0 makes the question undefined.
- Copy answer copies the result without thousands separators, so it pastes cleanly into a spreadsheet.
How to use the percentage calculator
- Under Calculation Type, press the question that matches yours, for example X is what % of Y?
- Type your two numbers into the labelled boxes. Commas, decimals and a leading minus sign are accepted.
- Read the Answer, then the Step-by-Step Solution and Formula Applied underneath.
- Press the copy icon beside the answer to take the number with you, or change a value and watch the answer update.
Quick check: 10% of a number is that number with its decimal point moved one place left, and X% of Y always equals Y% of X, so 8% of 50 is 50% of 8.
Who can use it
Shoppers working out a sale price, students checking homework, teachers marking and people comparing pay, prices or statistics can use it. Pair it with the discount calculator for sale prices, the grade calculator for weighted marks, or the tip calculator and split bill calculator at the table.
For business sums, the margin calculator and markup calculator turn a cost and a price into percentages, and the GST calculator, VAT calculator and income tax calculator handle tax. To see percentages compound over time, try the compound interest calculator. The scientific calculator takes longer expressions, and the calculators hub lists the rest.
Frequently asked questions (FAQs)
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 80 is 15 ÷ 100 × 80 = 12. In the calculator, choose "What is X% of Y?", type 15 as the Percentage and 80 as the Number, and the Solution panel shows the same two steps.
How do I calculate percentage increase or decrease?
Subtract the original value from the new value, divide by the original and multiply by 100. A salary that rises from 50,000 to 55,000 is up (55,000 − 50,000) ÷ 50,000 × 100 = 10%. A price that falls from 100 to 75 gives −25%. Use "Percentage change from X to Y" and enter the original value first.
What is the difference between percentage change and percentage difference?
Percentage change compares a new value with an original one, so direction matters: 80 to 100 is +25%, but 100 to 80 is −20%. Percentage difference has no baseline. It divides the gap by the average of the two values, so 80 and 100 differ by about 22.22% whichever you enter first.
How do I add or subtract a percentage from a number?
Multiply by (1 + P ÷ 100) to add P percent, or by (1 − P ÷ 100) to subtract it. 80 increased by 25% is 80 × 1.25 = 100, and 100 decreased by 25% is 100 × 0.75 = 75. The "Increase X by Y%" and "Decrease X by Y%" modes do this and show the intermediate amount.
How do I find the original number before a percentage was added?
Divide the final amount by (1 + rate). If something costs 120 after a 20% rise, the original was 120 ÷ 1.20 = 100. In the calculator, pick "X is Y% of what?" and enter 120 as the Part and 120 as the Percentage, because the new price is 120% of the old one.
What is the difference between a percent and a percentage point?
A percentage point is the plain gap between two percentages, while a percent change is relative to the starting figure. A rate that moves from 20% to 25% has risen 5 percentage points, which is a 25% relative increase because (25 − 20) ÷ 20 × 100 = 25. Always say which one you mean.
Is it safe to enter my numbers into this percentage calculator?
Yes. The sums run in your browser as you type, so the numbers are not uploaded or stored, and they disappear when you close or reload the page. You can verify this by opening the Network tab in your browser DevTools and watching that no request is made while you change the inputs.