How to use the Percentage Calculator
- Pick the question that matches your problem.
- Type your numbers into the sentence.
- Read the answer and the formula used to get it.
- Optional: apply consecutive percentage changes to see their combined effect.
Percentage formulas
- X% of Y = X ÷ 100 × Y. Example: 15% of 200 = 30.
- X is what % of Y = X ÷ Y × 100. Example: 30 is 25% of 120.
- Percentage change = (new − old) ÷ old × 100. Example: 80 → 100 is a 25% increase.
- Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100. It compares two values without treating either as the starting point.
Percentage change vs. percentage points
If an interest rate rises from 4% to 5%, it increased by 1 percentage point but by 25 percent. Mixing these up is one of the most common mistakes in news and reports.
Frequently asked questions
How do I calculate a percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100.
Why is a 50% drop followed by a 50% gain not break-even?
Because the gain is calculated on a smaller base. 100 → 50 (−50%) → 75 (+50%).