Calculators
Quick calculators for math, health, date and unit conversions.
Which tool do I need?
Small calculators for the sums people look up most, each showing how the answer was worked out so you can check it or use the same method on paper.
Percentages, discounts and percentage change
Exact age in years, months and days, or the gap between two dates
Width and height for a ratio like 16:9 or 4:5
Questions
- How do I work out percentage change?
- Subtract the old value from the new one, divide by the old value and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% up; from 100 back to 80 is 20% down.
- How is age calculated for forms?
- Most forms count completed years on a given date, often a cut-off date in the notice, not today. The age calculator lets you pick that date.