Percentage calculator
Choose a calculation type, enter your numbers, then press Calculate.
Results
These are estimates based on your inputs.
› How this calculator works
X% of Y = (X ÷ 100) × Y
X is what % of Y = (X ÷ Y) × 100
Percentage change = ((new − old) ÷ old) × 100
What this calculator does
This percentage calculator covers three common questions: X percent of Y, X is what percent of Y, and percentage change between two values. It provides the result and a simple working line so you can sanity-check the math.
It is useful for discounts, markups, performance changes, VAT calculations, or everyday maths.
How the formula works
The calculator uses standard percentage formulas. For X percent of Y, we multiply Y by X divided by 100. For X is what percent of Y, we divide X by Y and multiply by 100. For percentage change, we divide the difference by the original value and multiply by 100.
The working line shown below the result mirrors these formulas with your numbers filled in.
Worked example
Example: 20% of 250 is 50. The calculator shows 50 and the working line (20 ÷ 100) × 250.
For percentage change, if a price goes from 80 to 100, the change is (100 − 80) ÷ 80 × 100 = 25%.
Common mistakes
- Using the new value instead of the old value for percentage change.
- Forgetting to divide by 100 when calculating X percent of Y.
- Mixing up X is what percent of Y with Y is what percent of X.
- Assuming a negative percentage is always wrong.
When to use this calculator
Use this for quick percentage calculations in shopping, finance, or reports. If you need VAT inclusive or exclusive calculations, use the VAT calculator for those specific formulas.
FAQs
What if the old value is zero?
Percentage change is undefined when the old value is zero. The calculator will not give a reliable result in that case.
Can I use decimals?
Yes. The inputs accept decimals and the output rounds to two decimal places.
Why is my percentage change negative?
A negative value means the new value is lower than the old value, which indicates a decrease.