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04 tools

Calculators

Percentages, BMI, loans and age.

01Percentage CalculatorWork out a percentage of a number, what percentage one number is of another, and the percentage change between two values.→02BMI CalculatorCalculate body mass index from height and weight, see the WHO category, and find the weight range that would put you in the normal band.→03Loan CalculatorWork out the monthly payment on a fixed-rate loan, plus total interest and a year-by-year amortisation schedule.→04Age CalculatorFind your exact age in years, months and days, plus the total number of days lived and how long until your next birthday.→

Everyday arithmetic with the assumptions made visible

These four calculators cover the sums people get wrong most often, not because the arithmetic is hard but because the question is ambiguous. "20% off, then another 20% off" is not 40% off. A BMI of 25 means different things under WHO global, WHO Asia-Pacific and Chinese thresholds. A loan's advertised rate is not its APR. Each tool states which convention it is applying rather than picking one silently.

What the numbers are, and are not

A percentage is always a percentage of something, and the base is where errors live — a discount applies to the reduced price, VAT applies to the net figure. BMI is a population statistic applied to one person: it cannot distinguish muscle from fat, and it misreads very tall and very short bodies by construction. The honest use of any of these is as a trend over time, not as a verdict on a single day.

Nothing here is financial or medical advice

The formulas are standard and the arithmetic is exact, but a calculator cannot see your circumstances. Treat the output as a starting figure to check against a professional, not as a conclusion.