Percentage Calculator – Percent Of, Change & More
Pick a mode, enter your numbers, and read the result with the formula shown underneath.
Percentages show up in discounts, grades, tips, and growth rates. This calculator handles the common cases so you do not have to rearrange formulas by hand — pick a mode and type the numbers.
Formulas by mode: % of → Y × (X ÷ 100);Is what % → (X ÷ Y) × 100;Change → ((new − old) ÷ old) × 100;Points → point difference is new% − old%, and relative change of those rates uses the same percent-change formula;± by % → value × (1 ± percent ÷ 100).
Need tip math for a restaurant check? Try the Tip Calculator or Bill Split Calculator. Everything here runs in your browser.
How to use
- Choose a mode: % of, Is what %, Change, Points, or ± by %.
- Enter the values in the labeled fields (labels change with the mode).
- Read the primary answer and the formula line. Toggle More precision for four decimal places.
- Use Reset to clear and return to “% of”.
Tips
- For a discount, use “% of” on the original price to get the dollar amount off, then subtract from the original for what you pay — or use “± by %” with Decrease.
- Percent change can be negative when a value drops. That is different from percentage points (see the Points mode).
- When money is involved, two decimal places is usually enough. Use More precision when you need finer detail.
- Division by zero is not defined — if the “of” value or starting value is zero, you will see a clear message instead of a fake number.
FAQ
How do I find what percent one number is of another?
Divide the part by the whole, then multiply by 100. Example: 25 ÷ 100 × 100 = 25%, so 25 is 25% of 100. Use the “Is what %” mode.
What is “X% of Y”?
Multiply Y by X ÷ 100. Example: 18% of 80 is 80 × 0.18 = 14.4. Use the “% of” mode.
What is percent change?
Percent change compares an old value to a new one: ((new − old) ÷ old) × 100. A rise from 50 to 75 is a 50% increase. A drop from 75 to 50 is about a 33.33% decrease.
What is the difference between percentage points and percent?
If a rate goes from 10% to 12%, that is an increase of 2 percentage points. Relative percent change of those rates is (12 − 10) ÷ 10 × 100 = 20%. The Points mode shows both.
How do I increase or decrease a number by a percent?
Increase: new = value × (1 + percent ÷ 100). Decrease: new = value × (1 − percent ÷ 100). Example: 200 increased by 15% is 230. Use the “± by %” mode.
Why can’t I divide by zero?
Percent formulas need a non-zero “whole” or starting value. If that value is zero, the calculator shows an error instead of Infinity or NaN.
Can I use negative numbers?
Yes where the math still makes sense (for example, percent change between negative balances). Results follow standard arithmetic; check the formula line if a sign looks surprising.