％ Percentage Calculator
By ToolNimba Editorial Team · Updated 2026-06-19
Percentages turn up everywhere, discounts, tips, tax, exam scores, interest and statistics. This calculator covers the three questions people ask most: what is X% of Y, X is what percent of Y, and what is the percentage change from one value to another. Type your numbers and the answer updates as you go, with the working shown so you can learn the method, not just the result.
What is the Percentage Calculator?
A percentage is just a fraction with a fixed denominator of 100. The word comes from the Latin per centum, "per hundred", so 25% literally means 25 out of every 100, or the fraction 25/100, or the decimal 0.25. That single idea is the key to every percentage calculation: once you can move between a percent, a fraction and a decimal, the rest is ordinary multiplication and division.
Most real questions reduce to one of three shapes. Finding a part asks "what is 20% of 150?" and is solved by turning the percent into a decimal and multiplying: 0.20 × 150 = 30. Finding the rate asks "30 is what percent of 150?" and reverses that: divide the part by the whole and multiply by 100. Finding the change compares a before and an after value, the new minus the old, divided by the old, times 100, and tells you how much something grew or shrank in relative terms.
The reason percentages are worth a dedicated tool is that they are deceptively easy to get slightly wrong. Mixing up which number is the "whole", chaining a discount and a tax in the wrong order, or assuming an increase and a decrease of the same size cancel out are all common traps. Showing the working, not just the final number, is the fastest way to catch those mistakes before they cost you money or marks.
When to use it
- Working out a sale price: a 30% discount on a $80 jacket means you pay 70% of $80 = $56.
- Tipping at a restaurant: a 18% tip on a $45 bill is 0.18 × 45 = $8.10.
- Adding sales tax or VAT: an 8% tax on a $250 purchase adds 0.08 × 250 = $20, for a $270 total.
- Turning an exam score into a grade: 57 correct out of 75 questions is (57 ÷ 75) × 100 = 76%.
- Reading statistics and reports: comparing this year’s figure to last year’s as a percentage change rather than a raw difference.
How to use the Percentage Calculator
- Pick the calculation you need using the three tabs.
- Enter your two numbers in the boxes.
- Read the answer and the step-by-step working below it.
Formula & method
Worked examples
A $120 pair of shoes is marked 25% off. What do you pay?
- Discount = 25% of 120 = 0.25 × 120 = 30
- Price paid = 120 − 30 = 90
- Shortcut: paying 75% → 0.75 × 120 = 90
Result: You pay $90 (a $30 saving).
You scored 57 out of 75 on a test. What percentage is that?
- Divide the part by the whole: 57 ÷ 75 = 0.76
- Multiply by 100: 0.76 × 100 = 76
Result: 76%.
Monthly revenue rose from $80,000 to $100,000. What is the percentage change?
- Difference = 100,000 − 80,000 = 20,000
- Divide by the old value: 20,000 ÷ 80,000 = 0.25
- Multiply by 100: 0.25 × 100 = 25
Result: A 25% increase.
Common percentages of round numbers
| Percent | of 50 | of 100 | of 200 |
|---|---|---|---|
| 10% | 5 | 10 | 20 |
| 15% | 7.5 | 15 | 30 |
| 20% | 10 | 20 | 40 |
| 25% | 12.5 | 25 | 50 |
| 50% | 25 | 50 | 100 |
Common mistakes to avoid
- Assuming a 50% drop then a 50% rise returns to the start. It does not. Start at 100, fall 50% to 50, then rise 50% of 50 (which is 25) and you reach 75, not 100. The percentages act on different bases, so equal-sized up and down moves never cancel out. To undo a 50% drop you need a 100% rise.
- Confusing percentage points with percent. A rate moving from 4% to 6% is a rise of 2 percentage points, but a 50% increase. Reporting it as “up 2%” is wrong.
- Using the wrong number as the “whole”. For percentage change, always divide by the original (old) value, not the new one. Dividing by the new value gives a different, and incorrect, answer.
- Forgetting that stacked discounts do not add. Taking 20% off then a further 10% off is a 28% total discount, not 30%, because the second cut applies to the already-reduced price.
Glossary
- Percent
- A number expressed as a fraction of 100. 25% means 25 per hundred, i.e. 25/100 or 0.25.
- Percentage point
- The plain arithmetic difference between two percentages. Going from 10% to 15% is a rise of 5 percentage points (but a 50% relative increase).
- Percentage change
- How much a value grew or shrank relative to its starting value: (new − old) ÷ old × 100, expressed as a percent.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 20% of 150 is (20 ÷ 100) × 150 = 30.
What is X% of Y?
X% of Y equals (X ÷ 100) × Y. So 30% of 80 is (30 ÷ 100) × 80 = 0.30 × 80 = 24. A quick mental trick: 10% of any number is just that number with the decimal point moved one place left.
How do I find what percentage one number is of another?
Divide the first number by the second, then multiply by 100. For example, 30 out of 120 is (30 ÷ 120) × 100 = 25%.
What is the difference between percentage change and percentage difference?
Percentage change has a clear before and after, so you divide by the original value: from 80 to 100 is a +25% change. Percentage difference compares two values with no “starting point”, so you divide by their average: the difference between 80 and 100 is 20 ÷ 90 × 100 ≈ 22.2%.
How do I convert a percentage to a decimal?
Divide the percentage by 100, which is the same as moving the decimal point two places to the left. So 75% becomes 0.75, 8% becomes 0.08, and 150% becomes 1.5. To go the other way, multiply the decimal by 100.
Is this percentage calculator free?
Yes. Every ToolNimba tool is free, needs no sign-up, and runs entirely in your browser, so your numbers never leave your device.