Percentage Calculator

What is Percentage Calculator?

The Percentage Calculator is a free online tool that answers the percentage questions people ask most, across seven modes. The three basic modes find X% of Y, what percent X is of Y, and the percent change from X to Y. The increase/decrease mode applies a percentage up and down to a base value; the reverse mode recovers the original amount before a percentage markup or discount; the point-difference mode separates a percentage-point gap from a relative percent change; and the proportion mode solves A : B = C : ? for the missing fourth term. Pick a mode, type the numbers, and read each answer in a copyable read-only field with a step-by-step calculation shown beneath it. Results are formatted for your locale with up to six decimal places.

How to use Percentage Calculator

1. Pick a mode with the segmented buttons: X% of Y, X is what % of Y, % change, increase/decrease, reverse %, point difference, or proportion.
2. Type the first value into the top input and the second into the next; the labels change to match the chosen mode.
3. In proportion mode, fill the third input (C) so the tool can solve A : B = C : ?.
4. Read each answer in its read-only result field and press Copy to send it to the clipboard.
5. Check the worked calculation below the results to see exactly how each number was derived.
6. Switch modes at any time to reuse the same numbers for a different question.

Examples

Mode: Increase/Decrease, Y = 150, X = 20

Increased 180, decreased 120

Mode: Reverse %, value = 120, X = 20

Before a 20% increase 100, before a 20% discount 150

Mode: Proportion, A = 2, B = 3, C = 10

15

Frequently asked questions

What do the four new modes add beyond the basics?

Increase/decrease applies a percentage up and down to a value (150 ±20% = 180 or 120). Reverse % finds the original amount before a markup or discount (120 after a 20% discount came from 150). Point difference separates a percentage-point gap from a relative change. Proportion solves A : B = C : ? for the missing fourth term.

What is the difference between a percentage-point gap and a percent change?

Going from 30% to 45% is a gap of 15 percentage points but a relative increase of 50%. The point-difference mode shows both numbers so you never confuse the two.

How does reverse percentage work?

Enter the final value and the percentage. The tool divides by (1 + X ÷ 100) to undo an increase and by (1 − X ÷ 100) to undo a discount, showing both possible original values.

What happens if I enter zero or leave a field blank?

Empty or invalid fields show a dash. Modes that divide — what percent, percent change, point difference, reverse, and proportion — need their divisor to be non-zero, so those results stay blank until you supply a valid value.

Are my numbers sent to a server?

No. Every mode runs 100% client-side in your browser with no upload and no server communication, so the numbers you type never leave your device.