🧮 Math Calculators
Percentage, age calculator and Roman numerals
Calculate percentages — tip calculator, discount calculator, percentage increase and more.
Open tool →Calculate your exact age from any birth date. How old am I today?
Open tool →Convert numbers to Roman numerals and back. Free Roman numeral converter.
Open tool →Calculate speed, distance, or time from the other two. Free SDT triangle calculator.
Open tool →Add, subtract, multiply and divide fractions with step-by-step solutions.
Open tool →Calculate your GPA from course grades and credit hours.
Open tool →Calculate tip amount and split the bill between people.
Open tool →Convert numbers to written words for checks and invoices.
Open tool →Everyday arithmetic that is quicker to check than to do in your head — percentages, fractions, ratios of speed and distance, ages, tips, and numbers written out in words.
Each shows the working, which is the useful part. Percentage change in particular is a calculation most people can do and many get backwards, and seeing the expression makes the direction obvious.
Which tool do I want?
| If you… | Use |
|---|---|
| Percentage of, change between, or increase and decrease | Percentage Calculator |
| You need to simplify or convert a fraction | Fraction Calculator |
| Two of speed, distance and time are known | Speed, Distance & Time |
| You need an exact age or a duration in years | Age Calculator |
| You are splitting a bill | Tip Calculator |
| You need a figure written out for a cheque or contract | Number to Words |
| You are converting Roman numerals | Roman Numerals |
| You are working out a grade average | GPA Calculator |
A 20% fall does not undo a 20% rise
Percentages are taken from whatever the current value is, so the base moves. Take 100, add 20% to get 120, then remove 20% — that 20% is now of 120, so you lose 24 and land on 96. To get back to 100 you would need 16.7%.
The same asymmetry runs through anything measured in percentages. An investment down 50% needs 100% to recover. A price cut by 30% needs a 43% increase to return to where it was.
Related, and worth keeping separate: percentage points versus percent. An interest rate moving from 2% to 3% has risen by one percentage point and by 50 percent. Both are correct, they describe the same change, and choosing whichever sounds more dramatic is a standard trick in reporting.