Calculators
Everyday calculators for dates, health, and numbers. 18 tools
Arithmetic that is easy to get subtly wrong: percentages in both directions, what a loan actually costs once interest compounds, an age in years and days, the same moment in two time zones, the right split on a bill.
Each shows the working rather than only the answer, which matters when the result is going into something you have to defend — a quote, an invoice, or a deadline.
All 18 calculators
Percentage Calculator
Work out percentages, increases, decreases, and shares.
Age & Date Difference Calculator
Calculate exact age or the time between any two dates.
BMI Calculator
Calculate body mass index in metric or imperial units.
Unit Converter
Convert length, weight and temperature — mm to inches, kg to pounds, Celsius to Fahrenheit.
Loan / EMI Calculator
Calculate monthly payments, total interest, and payoff schedule.
Tip Calculator
Work out the tip and split the bill between people.
Random Number Generator
Generate random numbers in any range, with or without repeats.
Calorie Calculator
Estimate the calories you burn a day, and what to eat to lose, gain or maintain.
LCM & GCF Calculator
Find the lowest common multiple and greatest common factor of any set of numbers.
Volume Calculator
Work out the volume of a box, cylinder, sphere, cone, capsule or pyramid, in litres too.
Grade Calculator
Work out your weighted grade so far, and the score you need on what is left.
Date Calculator
Find the date a number of days from another, or count the days between two dates.
Printable Calendar
A calendar for any year or single month, ready to print or save as a PDF.
Dice Roller
Roll any number of d4 to d100 dice with a modifier, and keep the last twenty results.
Compound Interest Calculator
Project savings growth with compounding and monthly contributions.
Aspect Ratio Calculator
Scale width and height while keeping the same aspect ratio.
Time Zone Converter
A world clock that converts a time across cities and shows the difference at a glance.
Pomodoro Timer
Focus timer with work/break cycles and session tracking.
What to know before you pick one
A calculator is only as good as its assumptions
Two loan calculators disagreeing usually means they assume different things, not that one is broken: whether interest compounds monthly or daily, whether a payment lands at the start or end of the period, how a part-month is handled. Where a calculation on this page depends on an assumption, the page says which one it makes. Before relying on a figure for anything that matters, check that its assumption matches your actual agreement.
What an EMI figure does and does not tell you
A monthly instalment is the smallest useful number and the least informative one. The figures that change decisions are the total interest paid over the full term, and how that total moves when the term changes: a longer term lowers the monthly figure and raises the total, sometimes substantially. Comparing two offers on the monthly payment alone is how people end up paying more for the option that felt cheaper.
Percentages are where most everyday errors happen
A rise of 20% followed by a fall of 20% does not return you to where you started, because the second percentage applies to a larger number. A discount applied before tax gives a different total from the same discount applied after. These are not edge cases — they are the ordinary arithmetic of prices and salaries, and they account for most of the mistakes people make by hand.
Dates and times carry hidden rules
Working out the gap between two dates has to account for leap years, months of unequal length, and whether both endpoints count. Add time zones and daylight saving and the same instant can be two different calendar days. This is why an age or duration worked out in your head often disagrees by a day with one worked out properly.
Nothing you enter is transmitted
Every calculator here runs in the browser, so the figures stay on your device. That is deliberate for this category in particular: loan amounts, salaries, ages and health measurements are exactly the sort of details that should not be sitting in someone else’s server log because you wanted a quick answer.