Why Use This Tool?
Percentages trip people up because '15% of 200', '50 is what percent of 200' and 'the price went from 80 to 100' are three different operations. This page gives each its own panel so you never apply the wrong formula.
The percent change panel is the one discounts, raises, and analytics dashboards need — it shows direction (increase or decrease) as well as the size of the change.
How It Works
- Pick the panel that matches your question.
- Enter the two numbers it asks for.
- Read the result — direction is included for percent change.
Frequently Asked Questions
How do I calculate X percent of a number?
Multiply the number by the percentage divided by 100 — 15% of 200 is 0.15 × 200 = 30. The first panel does this directly.
How is percent change calculated?
(new − old) ÷ old × 100. Going from 80 to 100 is a +25% increase; the sign and label are both shown in the result.
Why is percent change from zero undefined?
The formula divides by the starting value — from zero there's no baseline, so any change is mathematically infinite.
Tips & Things to Watch
- A 50% increase followed by a 50% decrease does not return to the start — 100 → 150 → 75.
- Percent points vs percent: going 10% → 12% is 2 points but a 20% change.
- Double-check which value is the denominator — flipping X and Y flips the answer.