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Money
- Compound interest calculator Work out how much your savings will grow with compound interest and regular contributions, and how much of that total came from interest rather than from you.
- How much to save each month Say what you want and when. We work out the monthly amount, and how much of it the return contributes instead of you.
- Rental yield calculator Gross yield is the number in the advert. Net yield, after costs and empty months, is the one you actually get.
- Rule of 72 calculator The mental shortcut everyone knows, next to the exact answer. And how much the shortcut is off by at your rate.
- Simple interest calculator Simple interest always pays on the original capital and never on what you have already earned. Here it sits next to compound, which is where the difference shows.
- CAGR calculator Two figures and a term give the constant rate that would have taken the first to the second. It is the honest way to compare investments of different lengths.
- ROI calculator ROI is a simple division that gets misused constantly: 50% in six months and 50% in ten years give the same figure. So here it comes annualised too.
- Loan payment calculator Work out the monthly payment on a loan or mortgage and, above all, how much you will end up paying in interest.
- Loan amortisation schedule Every payment broken down. The interesting part is not the total, it is watching how long it takes before you are mostly paying off the debt.
- Early repayment: term or payment One lump sum, two ways to use it. Which saves more interest is not close, but the other one has its reasons.
- How much mortgage can I afford Two things limit you: what you can pay each month and what you have saved. We tell you which one is binding, because that decides what to do about it.
- From nominal rate to APR The nominal rate is what they advertise; the APR is what compares. Here is the real APR, with the arrangement fee spread across the life of the loan.
- Debt-to-income ratio The figure a lender looks at before any other. Not how much you earn, but how much of it is already spoken for.
Home and energy
- Appliance running cost calculator Power rating, hours of use and your electricity price. That is enough to know what any appliance is really costing you.
- Standby power cost calculator The devices you never really switch off. Individually trivial, and together a line on your bill that nobody looks at.
- Is it worth replacing that appliance The efficient one costs more today and less every year. Whether that trade works out depends on numbers, and usually it is closer than the shop suggests.
- Paint calculator for a room Room dimensions, number of coats and the area of doors and windows. We give you litres, tins and cost.
- Floor tile calculator Room size and tile size. We give you tiles, boxes and cost, with the wastage that cuts and breakages actually need.
- Air conditioner size calculator A rule of thumb for what size unit to look for, adjusted for the things that actually change the answer.
Dates and time
- Days between two dates calculator Enter two dates and we tell you how many days lie between them, broken down into weeks, spare days and hours.
- Difference between two dates in years, months and days Rather than counting loose days, this gives you the difference the way you would say it out loud: "2 years, 3 months and 5 days".
- Working days between two dates Count only the real working days between two dates: weekends come out, and public holidays too if you want them to.
- Add or subtract days from a date Give me a date and how many days to add or subtract. Count every day, or working days only.
- Exact age calculator Enter a date of birth and we work out the exact age in years, months and days, plus how long is left until the next birthday.
- Work hours calculator With your start time, finish time and break, we work out the effective day and what it adds up to over a week, a month and a year.
- Week number of the year Which week of the year a date falls in, under ISO 8601, which is the standard businesses use and does not always match what you would guess.
- What day of the week a date falls on What day you were born on, what day your birthday falls on, when a deadline lands. With the week number and the days between it and today.
Cars and travel
- Real fuel economy calculator Fuel put in and distance covered. That is all it takes to know what your car really does, rather than what the trip computer claims.
- Cost per unit of distance of your car Fuel is the part you notice and the smallest part of the bill. This adds the ones you do not: insurance, tax, servicing and, above all, depreciation.
- Compare the fuel cost of two cars Two cars, two consumption figures, two fuel prices. What the difference actually adds up to over the years you will keep it.
- Electric car charging cost What a charge costs and how far it takes you. Including the energy you pay for that never reaches the battery, which nobody mentions.
- What a trip costs in fuel Distance, consumption and fuel price. What the trip really costs, tolls included, and whether the train was cheaper after all.
- Split the cost of a trip The awkward conversation, settled with a number. Fuel, tolls and extras split between everyone, or everyone except the driver.
Sport
- Running pace calculator Give me any two of them and I give you the third, plus the split table to take to the race.
- Your equivalent time at another distance From one recent result we estimate what you could do at any other distance. And we tell you when not to trust it.
- Splits for your race Your target time shared out kilometre by kilometre. With the option to plan a negative split, which is how the good races get run.
- Heart rate training zones Your five training zones in beats per minute, and what each one is for. With the heart-rate-reserve method if you have your resting figure.
- Swimming pace calculator Your pace per 100 metres, which is how swimming is measured, plus your time per length and what you would do over other distances.
Health and body
- Body mass index calculator BMI is a one-line number that gets used constantly and understood rarely. Here it comes with the weight range for your height, and with the part the formula misses.
- Ideal weight for your height There is no ideal weight, there are four formulas that give four different numbers. Here they are together, with the BMI range alongside, so the real spread is visible.
- Body fat percentage A tape measure and three measurements give a body fat estimate that says considerably more than BMI, because this one does know what your weight is made of.
- Daily calories you need How many calories you burn a day given your body and your activity, and the figure that matches each goal. Using the real 7,700 kcal per kilo, not the rounded "500 a day".
Percentages and maths
- 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.
- 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.
- 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.
Business and pricing
- Straight-line depreciation How much you can write off each year on a van, a laptop or a machine, and what it is worth on the books at every point.
- CPM, CPC and cost per conversion The four figures a campaign gets judged on, worked out at once, with what each one actually means. Because a low CPC with a bad CTR is not good news.
- Profit margin calculator Margin and markup come from the same two numbers and are not the same size. Here you get both at once, which is the only way to stop confusing them.
- Markup calculator Put a percentage on your cost and out comes the price. And next to it, the margin you actually keep, which is always smaller and almost nobody works out.
- Sales commission calculator Base pay, percentage, and the threshold where it starts counting. With the effective percentage at the end, which is the only way to compare two offers.
Developers
- Base64 encoder and decoder Text to Base64 and back again. With real UTF-8, which is where half the home-made implementations fall over.
- URL encoder and decoder For putting text into an address without breaking it. The difference between encoding a value and encoding a whole URL is the bit that usually goes wrong.
- Character, word and byte counter Characters, words, lines and bytes. Counted properly: an emoji is one character, whatever your editor says.
- JSON formatter and validator Paste the JSON, pick an indent, done. If something is off we tell you exactly where, and how many keys and how deep it goes.
- JSON to YAML converter Paste the JSON and out comes the YAML. We quote the strings YAML would read as a boolean or a number, which is where nearly every surprise comes from.
- JWT decoder Paste the token and see what is inside. Note: this decodes it, it does not verify it — checking the signature needs the key.
- Number base converter Binary, octal, decimal and hex, both ways. With genuinely large integers: 64-bit values come out exact.
- Data size converter Bytes, KB, MB, GB… and KiB, MiB and GiB too. Both systems side by side, which is the only way to see why your 1 TB drive shows 931 GB.
- Unix timestamp converter Timestamp to date and date to timestamp. If the number is in milliseconds we spot it, which is the mistake that wastes the most time.
- HEX, RGB and HSL colour converter Hexadecimal, RGB and HSL, all three ways. Plus the contrast, which is what decides whether readable text fits on top.