What is a percentage calculator?
A percentage calculator solves the three questions people ask most often: how much is a given percent of a number, what percent one number is of another, and by what percent a value has increased or decreased.
Shoppers use it to check discounts, students for marks and homework, business owners for margins and tax, and anyone comparing prices, savings or growth.
The three calculations with examples
X% of Y is Y multiplied by X and divided by 100. For example, 15% of 80 is 12. To find what percent one number is of another, divide the part by the whole and multiply by 100: 30 out of 120 is 25%.
Percent change is the new value minus the old value, divided by the old value. From 50 to 65 is a rise of 30%. From 65 back to 50 is a fall of about 23.08%, which shows that percent change is not symmetric because the starting value is different.
Everyday uses
Percentages are everywhere: sale prices, exam marks, interest rates, tax, tips, battery levels and population growth. Shoppers use the calculator to see whether a 30% discount beats a 20% discount plus a coupon. Students convert marks into percentages to compare subjects with different totals. Small business owners work out profit margin and markup. Because the answer updates as you type, you can try several numbers quickly and see how each one changes the result without reaching for pen and paper.
How to use it
- Choose the card that matches your question.
- Type the two numbers. The answer updates as you type.
- Read the result under the boxes. A negative change means a decrease.
- Clear the boxes and try another case.
Practical tips
- To work out a sale price, calculate the discount with the first card and subtract it from the original price.
- For an exam score, use the second card with your marks as the part and the total marks as the whole.
- For price changes, put the old price first and the new price second.
- Do not confuse a percent with a percentage point. Going from 10% to 12% is a rise of 2 percentage points but 20% in relative terms.
Frequently asked questions
How do I calculate X% of Y?
Multiply Y by X and divide by 100.
What if the old value is zero?
Percent change from zero is undefined, so the tool shows a dash.
Can I use decimals and negatives?
Yes, both work.
Why does a 50% rise then 50% fall not return to the start?
The second percentage is taken from a larger number.
Is anything sent to a server?
No. All maths happens in your browser.