Basic Utilities Calculators
Quick calculators for everyday arithmetic — percentages, discounts, tips, dates and unit conversions.
Age Calculator
Calculate exact age in years, months, days.
Basic Calculator
Standard arithmetic operations.
Measurement Converter
Convert length, weight, area & volume.
Percentage Calculator
Calculate percentages and changes.
Date & Time
Calculate durations between dates.
Tip Calculator
Calculate tips and split bills.
Salary Converter
Convert hourly, daily, annual wages.
50/30/20 Budget
Split your income into needs, wants, and savings.
Currency Converter
Live exchange rates for world currencies.
Small calculations, frequently done wrong
Percentage change is the most commonly reversed calculation in everyday use. A price that rises 20% and then falls 20% does not return to where it started — it ends about 4% lower, because the second percentage applies to a larger base. The same asymmetry explains why a 50% investment loss requires a 100% gain to recover.
Stacked discounts work the same way. "30% off, then an extra 20% off" is not 50% off. It is 44% off, because the second reduction applies to the already-discounted price. Retailers rely on the intuition being wrong in their favour.
Date arithmetic is less obvious than it looks once leap years and varying month lengths are involved. The age and date calculators here handle both correctly rather than approximating a year as 365 days.
Each of these runs instantly in your browser with no signup and works on mobile, which is usually where you need them.