Calculators that show their working
66 free tools for health, money, dates, maths and everyday problems. Every one states the formula it uses and walks through a worked example, so you can check the answer by hand if you want to. Nothing you type is ever sent anywhere — it is all computed in your browser.
Health & Fitness
Body composition, energy requirements, training zones and the everyday health numbers people actually look up — with the limits of each formula stated plainly.
BMI Calculator
Enter your height and weight to get your body mass index, the WHO category it sits in, and the weight range that would put you in …
Health & FitnessBMR Calculator
Your BMR is the energy your body spends just staying alive: breathing, circulating blood, maintaining temperature and repairing ce…
Health & FitnessTDEE Calculator
TDEE is your maintenance level: eat that many calories and your weight holds steady. Everything else in nutrition planning is meas…
Health & FitnessBody Fat Percentage Calculator
No scales or scanners needed — the US Navy method estimates body fat from neck, waist and (for women) hip circumferences, which is…
Health & FitnessIdeal Weight Calculator
There is no single ideal weight, and the four formulas below will give you four different answers. That disagreement is the most u…
Health & FitnessLean Body Mass Calculator
Lean body mass is everything that is not fat: muscle, bone, organs, water and connective tissue. It is what you want to keep while…
See all 21 health & fitness calculators →
Finance & Money
Loans, savings, interest, salary and the arithmetic of everyday money decisions, worked through step by step rather than hidden behind a black box.
Compound Interest Calculator
Compounding is interest earning interest. Over short periods it is barely noticeable; over decades it does most of the work.…
Finance & MoneyLoan Calculator
The monthly payment is the number lenders advertise. The total interest is the number that decides whether the loan is good value.…
Finance & MoneyMortgage Calculator
A mortgage is usually the largest loan anyone takes and the one where small differences in rate compound into very large amounts o…
Finance & MoneyCredit Card Payoff Calculator
Minimum payments are calculated to be affordable, not to clear the debt. On a typical card they can keep a balance alive for well …
Finance & MoneySavings Goal Calculator
Turn a vague intention into a monthly number — the only form a savings goal survives contact with real life in.…
Finance & MoneyInflation Calculator
Inflation is the reason a salary that has not changed in five years is a pay cut.…
See all 14 finance & money calculators →
Maths & Numbers
Percentages, ratios, averages, geometry and algebra, each with the method written out so you can reproduce the answer without the calculator.
Percentage Calculator
Three questions, one page. Enter two numbers and get all the percentage relationships between them.…
Maths & NumbersPercentage Change Calculator
Change and difference are not the same calculation, and using the wrong one is a common source of misleading statistics.…
Maths & NumbersMean, Median and Mode Calculator
Three different things get called 'the average', and choosing between them can change the story a dataset tells.…
Maths & NumbersStandard Deviation Calculator
Standard deviation answers the question an average cannot: how spread out are these numbers?…
Maths & NumbersFraction Calculator
All four operations, with the working shown — including why division by a fraction means multiplying by its reciprocal.…
Maths & NumbersRatio Calculator
Ratios turn up in recipes, maps, mixing paint, splitting bills and scaling drawings — and all of it is the same arithmetic.…
See all 12 maths & numbers calculators →
Date & Time
Ages, durations, deadlines, working days and time zones — the calculations that are deceptively easy to get wrong by one day.
Age Calculator
Exact age is not a subtraction. Months have different lengths, so the answer depends on the order you count in.…
Date & TimeDate Difference Calculator
Two dates in, every useful measure of the gap out — including the inclusive and exclusive counts, which differ by one and cause en…
Date & TimeWorking Days Calculator
Contracts, notice periods and delivery estimates are almost always counted in working days, which is a different number from calen…
Date & TimeTime Duration Calculator
Built for timesheets: it handles overnight shifts, subtracts breaks, and gives the decimal hours that payroll systems expect.…
Date & TimeAdd or Subtract Days Calculator
Includes the end-of-month rule, which is where date arithmetic quietly goes wrong.…
Unit Conversion
Exact conversions between metric and imperial units, with the definitions and conversion factors the numbers come from.
Length Converter
Since 1959 the inch has been defined as exactly 25.4 millimetres, which makes every imperial length conversion exact rather than a…
Unit ConversionWeight Converter
Includes stones and pounds, which almost no international converter handles properly.…
Unit ConversionTemperature Converter
The only common conversion where you cannot simply multiply, because two of the scales do not start from the same zero.…
Unit ConversionSpeed Converter
Includes knots and Mach, plus the pace equivalents runners and cyclists actually use.…
Unit ConversionData Storage Converter
There are two competing definitions of a gigabyte, and the gap between them is exactly why a '1 TB' drive shows up as 931 GB.…
Unit ConversionVolume Converter
A US pint is 473 ml and a UK pint is 568 ml. Recipes and fuel figures both go wrong when that is missed.…
See all 7 unit conversion calculators →
Home & Everyday
Practical calculations for the house, the car, the kitchen and the shop — quantities, costs and the comparisons that save money.
Fuel Cost Calculator
The number that makes a long commute feel real, and the one people forget when comparing two cars.…
Home & EverydayElectricity Cost Calculator
Wattage times hours times tariff. The surprise is usually which appliances turn out to matter and which do not.…
Home & EverydayPaint Calculator
Buying one tin short halfway through a wall is worse than buying one too many — colour batches vary.…
Home & EverydayUnit Price Comparison
The bigger pack is usually cheaper per unit. Usually — and supermarkets rely on you assuming it always is.…
Home & EverydayGPA Calculator
A GPA is a credit-weighted average, which means a four-credit course counts twice as much as a two-credit one.…
Home & EverydayTile Calculator
The wastage allowance is the part people skip, and it is the reason so many tiling jobs stop one box short.…
See all 7 home & everyday calculators →
Why another calculator site
Most calculators on the web are a box that produces a number. You put figures in, a result appears, and you have no way of telling whether it is right, what assumptions it made, or why a different site gave you a different answer.
Every tool here does three additional things. It states the formula it applies, in notation you can follow. It works through an example with real figures, so you can verify the implementation yourself. And it says what the formula ignores — because every model simplifies, and knowing where the simplification bites is the difference between a useful estimate and false precision.
Your numbers stay on your device
There are no accounts, no logins and no saved profiles. The calculations run in JavaScript on your own machine, which means the weight, salary, loan balance or medical figure you type is never transmitted to us and never stored. You can verify this by opening your browser's network tab while using any tool on the site — nothing is sent. The site is free because it carries advertising, not because your data is the product. The details are in our privacy policy.