Percentage Calculator Online: Percent of, Change and Difference
Use this percentage calculator to find X% of a number, what percent one number is of another, percentage change, increase, decrease and difference. Results appear as you type, with the formula and working shown.
By Troopus · Updated: October 24, 2026
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Calculate any percentage online
What is a percentage of a number? For example, 20% of 150.
How to calculate percentage with a percentage calculator online?
To calculate a percentage, divide the part by the whole and multiply by 100. For example, 30 out of 120 is 30 ÷ 120 × 100 = 25%. Going the other way, X% of a number is the number multiplied by X and divided by 100. The calculator above does both and shows each step.
Whether you call it a percent calculator or a percentage calculator online, it solves one idea: a percentage is a fraction with a denominator of 100, so 25% means 25 out of every 100, or 0.25. Every percentage problem has three pieces: the part, the whole and the percentage. Know any two and you can find the third.
| You know | You want | Formula |
|---|---|---|
| Whole and percentage | Part | whole × percentage ÷ 100 |
| Part and whole | Percentage | part ÷ whole × 100 |
| Part and percentage | Whole | part × 100 ÷ percentage |
Pick the matching tab in the percentage calculator online above, type the two numbers you know, and the third appears as you type.
How do I find X% of a number?
To find X% of a number, multiply the number by X and divide by 100. For example, 20% of 150 is 150 × 20 ÷ 100 = 30. You can also turn the percent into a decimal first (20% = 0.20) and multiply: 150 × 0.20 = 30. Use this for tips, commissions and sales tax.
A mental shortcut: find 10% by moving the decimal point one place left, then scale. For 10% of 85 you get 8.5, so 20% is 17 and 5% is 4.25.
| Question | Working | Answer |
|---|---|---|
| 18% tip on a $64 bill | 64 × 18 ÷ 100 | $11.52 |
| 5% of 3,200 | 3,200 × 5 ÷ 100 | 160 |
| 12.5% of 80 | 80 × 12.5 ÷ 100 | 10 |
How do I find what percent one number is of another?
Use the second tab. If you answered 42 of 50 questions correctly, 42 ÷ 50 × 100 = 84%. If the part is bigger than the whole, the answer is above 100%: 150 is 125% of 120.
How do I find the whole from a part and a percentage?
Use the third tab, "X is Y% of what". If 30 is 25% of a number, the number is 30 × 100 ÷ 25 = 120. This is how you reverse a percentage to find the original amount.
How does a percentage calculator online find percentage increase or decrease?
Percentage change equals the new value minus the old value, divided by the old value, times 100. A price that rises from 80 to 100 gives (100 − 80) ÷ 80 × 100 = +25%. A negative result is a percentage decrease: falling from 100 to 80 is −20%.
The percentage change calculator tab uses one rule: the starting value is always the base, which is why a rise and a fall of the same size give different percentages. Going from 80 to 100 is +25%, but going back from 100 to 80 is only −20%.
| From | To | Working | Change |
|---|---|---|---|
| 50 | 65 | (65 − 50) ÷ 50 × 100 | +30% |
| 200 | 150 | (150 − 200) ÷ 200 × 100 | −25% |
| 12 | 30 | (30 − 12) ÷ 12 × 100 | +150% |
The starting value cannot be zero, because dividing by zero is undefined. If you start from a negative number, the calculator divides by its absolute value so that moving from −10 to −5 shows as an increase.
What is the difference between percentage change and percentage difference?
Percentage change compares a new value with an old one, so order matters; percentage difference compares two values with no starting point. Difference divides the gap by the average of both numbers. Between 80 and 120, the change from 80 is +50%, but the difference is 40 ÷ 100 × 100 = 40%.
Use percentage change when something moved over time: price, salary, traffic. Use percentage difference when you compare two things side by side, such as two phone prices or two test results where neither came first.
The formula for the percentage difference is |A − B| ÷ ((A + B) ÷ 2) × 100. Because it uses the average as the base, swapping A and B gives the same answer. That is why the percentage difference calculator tab has no "starting" and "ending" labels.
If you are unsure which to use, ask whether one number is the "before". If yes, use percentage change.
How do I add or subtract a percentage (discount, tax, tip)?
To add a percentage, multiply by (1 + percent ÷ 100); to subtract it, multiply by (1 − percent ÷ 100). A $480 item with 15% off costs 480 × 0.85 = $408. Adding 8% sales tax to $50 gives 50 × 1.08 = $54. Use the "Add or subtract %" tab for both.
| Case | Multiplier | Final amount |
|---|---|---|
| $480 with 15% off | × 0.85 | $408 |
| $50 plus 8% sales tax | × 1.08 | $54 |
| $64 plus 20% tip | × 1.20 | $76.80 |
To reverse a discount and find the original price, divide instead of multiplying. If the sale price is $408 after 15% off, the original is 408 ÷ 0.85 = $480. You can also reach the same answer with the "X is Y% of what" tab, using 85 as the percentage.
Successive discounts do not add up. 20% off followed by 10% off is 0.80 × 0.90 = 0.72, a total discount of 28%, not 30%.
Percentage formulas cheat sheet
Every percentage calculation is a variation of part ÷ whole × 100. Percent of a number is whole × % ÷ 100, percentage change is (new − old) ÷ old × 100, and the whole is part × 100 ÷ %. The table below lists each formula with a worked example.
| Task | Formula | Example |
|---|---|---|
| X% of Y | Y × X ÷ 100 | 15% of 60 = 9 |
| X is what % of Y | X ÷ Y × 100 | 9 is 15% of 60 |
| X is Y% of what | X × 100 ÷ Y | 9 is 15% of 60 |
| Percentage change | (new − old) ÷ old × 100 | 60 to 69 = +15% |
| Add a percentage | value × (1 + %/100) | 60 plus 15% = 69 |
| Subtract a percentage | value × (1 − %/100) | 60 minus 15% = 51 |
| Percentage difference | |A − B| ÷ avg(A, B) × 100 | 60 vs 69 = 14.0% |
The calculator accepts commas as thousands separators (1,250) and dots for decimals (12.5), and you can choose how many decimal places to show. Results are exact to the digits displayed.
Frequently asked questions
How do you calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 20% of 150 is 150 × 20 ÷ 100 = 30. You can also multiply by the decimal form: 150 × 0.20 = 30.
How do I use a percentage increase calculator?
Enter the old and new values, or by hand subtract the old value from the new one, divide by the old value, and multiply by 100. Going from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%. The old value must not be zero.
How do I use a percentage decrease calculator?
Enter the old and new values in the same tool, or use the formula for increase: (new − old) ÷ old × 100. A negative answer is a decrease. From 200 to 150 it is (150 − 200) ÷ 200 × 100 = −25%, meaning the value fell by 25%.
What is the formula for percentage difference?
Percentage difference is the absolute gap between two values divided by their average, times 100: |A − B| ÷ ((A + B) ÷ 2) × 100. For 80 and 120, that is 40 ÷ 100 × 100 = 40%.
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. For example, 45 is 45 ÷ 60 × 100 = 75% of 60. If the first number is larger than the second, the result is over 100%.
How do I calculate a discount percentage?
Subtract the sale price from the original price, divide by the original price, and multiply by 100. If something dropped from $800 to $600, the discount is (800 − 600) ÷ 800 × 100 = 25%.
How do I reverse a percentage to find the original number?
Divide the result by the remaining share as a decimal. If $408 is the price after a 15% discount, the original is 408 ÷ 0.85 = $480. Or use the "X is Y% of what" tab.
Is my data sent anywhere?
No. The calculation runs entirely in your browser, and the numbers you type are not uploaded or stored. You can disconnect from the internet after the page loads and it will still work.