Available now
Profit Calculator
Your real margin on eBay, Amazon and Shopify after every fee each one takes.
VAT Calculator
Add or remove VAT at 20%, 5% or a rate you set.
Percentage Calculator
Percentage of a number, increase, decrease and difference.
Being built next
In this order. Each one ships with its method shown, a worked example and an honest list of what it doesn't account for.
Everyday maths
Age Calculator
Exact age in years, months and days — or the gap between any two dates.
Ratio Calculator
Simplify a ratio, scale it up, or find the missing part.
Hours Calculator
Add up worked hours between two times, across days or a whole week.
Converting
Unit Converter
Length, weight, volume and temperature — cm to feet, kg to pounds and back.
Money
Compound Interest Calculator
What savings grow to, year by year, with the working shown.
Selling online
Margin & Markup Calculator
Turn cost into price, or price into margin — without the platform fees.
Health
BMI Calculator
Body mass index from height and weight, in metric or imperial.
Why another calculator site?
The working is shown
Every result comes with the arithmetic that produced it, using your own numbers. If you can’t follow it, we’ve failed.
The gaps are named
Each calculator says what it doesn’t model — VAT, fulfilment fees, returns. A tool that quietly overstates is worse than no tool.
Rates are dated
Fees and tax bands change every April. Every figure carries the year it came from, so you can tell when it’s gone stale.