Percentage Calculator — Calculate Percentages, Discounts & Changes Free
Five percentage calculation modes in one tool: find what X% of a number is, calculate what percent one number is of another, compute percentage change between two values, add or remove a percentage (tax, discount, markup), and find the percentage difference between two values. All calculations update in real time.
100% private. All calculations run locally in your browser. No data is collected or transmitted.
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How to Use the Percentage Calculator
- 01
Select a calculation mode
Choose from 5 modes: X% of Y, "is what percent", percentage change, add/remove %, or percentage difference.
- 02
Enter your values
Type the numbers into the input fields. Results calculate in real-time as you type — no need to press a button.
- 03
Save to history
Click the result to save it to the history strip. The last 5 calculations are kept so you can compare results.
Frequently Asked Questions
How do I calculate a percentage of a number?
To find X% of a number Y, multiply Y by (X/100). For example, 15% of 200 = 200 × 0.15 = 30. Use Mode 1 in this calculator — enter the percentage and the number, and the result appears instantly.
How do I calculate percentage change (increase or decrease)?
Percentage change = ((New Value − Old Value) / |Old Value|) × 100. For example, going from 80 to 100 is an increase of ((100 − 80) / 80) × 100 = 25%. Going from 100 to 80 is a decrease of ((80 − 100) / 100) × 100 = −20%. Use Mode 3.
What is the difference between percentage change and percentage difference?
Percentage change measures the change from one value to another — it has a direction (increase or decrease). Percentage difference measures how much two values differ relative to their average — it's symmetric (no direction). For 80 and 100: percentage change from 80 to 100 is +25%, but percentage difference is |80−100| / ((80+100)/2) × 100 = 22.2%.
How do I add a percentage (tax, tip, markup)?
To add X% to a value, multiply by (1 + X/100). For example, $80 + 20% tax = $80 × 1.20 = $96. Use Mode 4 (Add / remove %) with the + option. To remove a percentage (discount), use the − option: $100 − 25% = $100 × 0.75 = $75.
How do I calculate what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 is what percent of 200? Answer: (30 / 200) × 100 = 15%. This is useful for calculating test scores, completion rates, or what portion of a budget an item represents. Use Mode 2.
What is percentage difference used for?
Percentage difference is used when you want to compare two values without implying one is the "original." It's common in scientific comparisons, price comparisons, and quality control. Unlike percentage change, it treats both values equally and the result is the same regardless of which value you put first.