“20% of 500,” “100 is what percent of 500?” and “500 increased by 20%” look similar but require different calculations. Percentage Calculator helps separate those relationships so you can solve percent-of-value, part-to-whole, and percentage-change questions without rearranging formulas by hand.
The most important detail is the base value. For percentage change, the original value is the denominator; for percentage points, you are comparing two percentages directly. Keeping those ideas separate prevents common errors in discounts, exam scores, analytics, finance, and business reporting.
How to use this tool
Core percentage formulas
X% of Y: (X ÷ 100) × Y.
A is what percent of B: (A ÷ B) × 100.
Percentage change: ((new − original) ÷ original) × 100.
How to use the Percentage Calculator
- Choose the percentage relationship that matches your question.
- Enter the values in the matching fields.
- For percentage change, confirm which value is the original and which is the new value.
- Calculate the result and interpret it using the correct base.
- Round only the final result if a specific level of precision is required.
Percentage change versus percentage points
If a conversion rate rises from 10% to 15%, the absolute change is five percentage points. Relative to the original 10%, the increase is 50%. The two measurements answer different questions.
When percentage change is undefined
Standard percentage change cannot be calculated from an original value of zero because the formula would divide by zero. In that situation, report the absolute change or use a different comparison that fits the context.
Common mistakes to avoid
- Reversing the part and whole in a part-to-whole percentage.
- Using the new value as the denominator for percentage change.
- Confusing a percentage-point difference with a relative percentage change.
- Trying to calculate standard percentage change from a zero starting value.
- Rounding intermediate values too early.
- Comparing percentages calculated from different base values without saying so.
Examples
Find 20% of 250
20 ÷ 100 × 250 = 50.
What percent is 45 of 180?
45 ÷ 180 × 100 = 25%.
Percentage increase
(100 − 80) ÷ 80 × 100 = 25% increase.
Percentage decrease
(425 − 500) ÷ 500 × 100 = −15%, so the value decreased by 15%.
Percentage points vs relative change
The rate increased by 5 percentage points and by 50% relative to the original rate.
Common use cases
- Discount calculations
- Exam and test scores
- Sales and revenue growth
- Website conversion-rate changes
- Budget increases or reductions
- Survey shares
- Price changes
Frequently asked questions
How do I calculate X percent of a number?
Divide X by 100 and multiply by the number. For example, 20% of 250 is 0.20 × 250 = 50.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, 45 ÷ 180 × 100 = 25%.
How is percentage change calculated?
Subtract the original value from the new value, divide the difference by the original value, and multiply by 100: ((new − original) ÷ original) × 100.
Can a percentage be greater than 100%?
Yes. A percentage above 100% simply means the measured amount is greater than the selected base. For example, 150 is 150% of 100.
Can percentage change be negative?
Yes. A negative percentage change means the new value is below the original value. A move from 500 to 425 is −15%, which is a 15% decrease.
What happens when the original value is zero?
Standard percentage change is undefined because the formula requires division by the original value. Use the absolute change or another context-appropriate comparison instead.
What is the difference between percentage change and percentage points?
Percentage points measure the absolute gap between two percentages. Percentage change measures the relative movement compared with the original percentage.
Should I round percentage calculations?
Keep full precision during intermediate steps and round the final result only when necessary. Early rounding can create avoidable differences.