Calculators
Everyday maths with the working shown, so you can check the answer yourself. 8 free tools.
- Percentage CalculatorX% of Y, percentage change, and what percent one number is of another.
- Age CalculatorExact age in years, months and days from a date of birth.
- Scientific CalculatorTrig, logs, powers and roots, with keyboard input.
- Discount CalculatorSale price and savings, including stacked discounts.
- Average CalculatorMean, median, mode and range of a list of numbers.
- Fraction CalculatorAdd, subtract, multiply and divide fractions, simplified.
- GPA CalculatorGPA on a 4.0 scale from letter grades and credit hours.
- Ratio CalculatorSimplify a ratio or solve for the missing value.
Before you use them
Notes on calculators
Three mistakes these calculators help you avoid
Percent versus percentage points
If a rate goes from 4% to 5%, it rose by one percentage point, but by 25% of its old value. News reports mix the two up often. The Percentage Calculator shows both so you can quote the right one.
Stacked discounts don't add up
"20% off, then another 10% at the till" is not 30% off. The second discount applies to the already reduced price: 0.80 × 0.90 = 0.72, so you pay 72% and save 28%. The Discount Calculator handles any number of stacked discounts this way.
The average that hides the story
Five salaries of 30, 32, 35, 38 and 200 thousand have a mean of 67 thousand, which nobody in the group earns. The median, 35 thousand, describes the typical person far better. The Average Calculator gives mean, median and mode side by side for this reason.
Quick checks you can do in your head
| Situation | Result | Why |
|---|---|---|
| Up 50%, then down 50% | −25% | 1.5 × 0.5 = 0.75 |
| 20% off, then 10% off | −28% | 0.8 × 0.9 = 0.72 |
| Price after 15% tax is 115 | 100 before tax | 115 ÷ 1.15, not 115 − 15% |
| Doubling, as a percentage | +100% | The increase equals the original |
GPA scales vary between universities, especially for plus and minus grades. The GPA Calculator uses the common 4.0 scale and lets you change the points per grade to match your transcript.