Percentages and maths
Discounts, increases, proportions, VAT, averages and grades. Everyday maths, properly explained.
Whole numbers and fractions
2 tools- Fraction calculator The four operations on fractions, simplified at the end and with the intermediate step visible, which is where you see why the answer is what it is.
- Greatest common factor and lowest common multiple Both at once, for as many numbers as you like, with each one broken into primes alongside. Which is where you see why the answers are what they are.
Percentages and discounts
5 tools- Percentage calculator Enter a percentage and a number. Instead of making you pick an operation first, we give you all four answers at once.
- Percentage change calculator From one value to another, how much has it gone up or down in percent? And how many times one is of the other.
- Stacked discount calculator 50% and then an extra 20% is not 70%. Here you see the real final price and the single discount you are actually being given.
- VAT calculator Add VAT to a price, or strip it out of one that already includes it. With the net and tax split, which is what an invoice needs.
- What percentage one amount represents Two numbers, and we tell you what percentage the first is of the second. With the remainder and the ratio in plain language.
Proportions and averages
3 tools- Rule of three calculator Solve a direct or inverse proportion. We show the working, not only the result.
- Weighted average calculator Paste your values with their weights, one per line. We give you the weighted average, the simple one, and how much each item contributes.
- What grade do I need on the final Tell us what you have and how much it counts. We tell you what you need on the rest, and if it is already out of reach we say so plainly.
Other categories
- Money Compound interest, loans, mortgages and savings goals, with a breakdown of where every figure comes from and a chart of how it evolves.
- Home and energy What your appliances cost to run, what standby really adds up to, and how much material a room actually needs.
- Dates and time Days between dates, ages, working days, deadlines and hours worked. Instant results, no sign-up.
- Cars and travel Real fuel economy, what a trip costs, cost per mile and splitting the bill between everyone in the car.
- Sport Running paces, race-time equivalents, splits and training zones. For running with your head as well as your legs.
- Health and body Body mass index, healthy weight, body fat and daily calories, with the formula in plain sight and what each number leaves out.
- Business and pricing Margin, markup, commission, asset depreciation and what a campaign costs. The sums you do before setting a price.
- Developers Format JSON, encode and decode, convert bases and colours. The things you look up mid-afternoon with the editor open.