Why is 20% off not the opposite of +20%?

Percentages depend on the base amount: adding 20% to 100 yields 120, whereas subtracting 20% from 120 removes 24 and leaves 96.

Math & Statistics100% Client-Side · Instant Math

Percentage Calculator

Solve % of a number, % ratio, percentage change, and increase/decrease.

Percentage of a Value

What is

% of

Result Summary

What Percent Is X of Y?

is what % of

Result Summary

25%

Percentage Change (Increase / Decrease)

From Value

To Value

Percentage Change

+25.00%

Increase (30)

How to Use This Calculator

Three instant percentage modes in one clean view: calculate X% of Y, find what percent X is of Y, and compute percentage increase/decrease or markup/discount deltas.

1Use Mode 1 to compute what P% of a base value V equals.
2Use Mode 2 to determine what percentage part A represents out of total B.
3Use Mode 3 to compute percentage change (% increase or decrease) between starting and ending values.

Standard Formula & Methodology

Change % = ((New - Old) / |Old|) × 100 | P% of V = (P / 100) × V.

Helpful Context & Precision Notes

Includes a quick Tip & Discount helper and instant copy button on every calculated answer.

All inputs stay locally inside your browser tab — nothing is uploaded or logged.

Frequently Asked Questions

Subtract the original value from the new value, divide by the absolute original value, and multiply by 100. Mode 3 automates this with direction labels.