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Percentage Calculator

Every percent question, answered in one place.

Percent questions come in three flavors and everyone mixes them up: finding a percentage of a number, computing the percentage change between two numbers, and working out what percent one number is of another. This calculator has all three modes on one page with the formula visible in the labels — useful for homework, tips, price changes, and quick data checks.

Why people use this

Homework, tips, price changes, test scores, data at work — percent questions come in three forms and everyone mixes them up. People use this because it handles all three on one page without having to remember which formula goes where.

How it works

1. Mode 1 — "What is X% of Y": enter the percent and the value.
2. Mode 2 — "Percentage change": enter the starting and ending numbers.
3. Mode 3 — "X is what percent of Y": enter the part and the whole.
4. Each mode computes live as you type.

Common questions

What is the formula for percentage change?

(New − Old) ÷ |Old| × 100. Going from 80 to 120 is (120−80)÷80×100 = +50%. The vertical bars matter: change from a negative base needs the absolute value to keep the sign sensible.

If a price drops 20% then rises 20%, is it back where it started?

No. $100 − 20% = $80; $80 + 20% = $96. Percentage changes apply to the current value, so symmetric moves do not cancel — you end up 4% down.

What is the difference between percentage points and percent?

An interest rate rising from 3% to 4% is up 1 percentage point but up 33.3% in relative terms. News headlines routinely confuse the two; this calculator computes the relative (percent) version.

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