Calculators
Everyday maths for money, health, dates and statistics.
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About Calculators
Most calculations people actually need are not hard — they are just fiddly enough to get wrong in your head and annoying enough to set up in a spreadsheet. Working out a loan repayment, a percentage change, an age in exact years and months, or how much tax to add to an invoice.
These calculators cover the recurring ones: percentages, loan and mortgage repayments, compound interest, sales tax and VAT, discounts, ages and date differences, plus health measures like BMI and daily calorie needs, and the basic statistics functions.
Each calculator shows the formula it uses rather than just producing a number. This matters for two reasons. It lets you sanity-check the result against your own working, and it lets you understand what the number actually means — a BMI of 27 tells you very little unless you know what it is measuring and what it ignores.
A necessary caution: the financial and health calculators here produce estimates for planning purposes, not advice. Loan calculators cannot know your lender's specific fee structure, rounding conventions, or how they treat part-months. Health calculators use population-level formulas that do not account for individual circumstances such as muscle mass, pregnancy, or medical conditions. Use these to get oriented, then confirm anything that carries real consequences with your lender, accountant, or doctor.
Why your bank's number differs from this one
A loan calculator applies the standard amortisation formula to the rate, term and principal you enter. A lender's quote applies their own arrangement fees, their particular day-count convention, how they treat a part-month at the start of the term, and rounding rules that can shift each payment by a few units of currency. Small differences compound across hundreds of payments.
Advertised rates add another gap. A headline rate is often not the figure used to calculate repayments once compulsory insurance, account fees or a different compounding frequency are included — which is precisely what a comparison rate or APR exists to expose. Treat any calculated repayment as an estimate accurate to within a percent or two, useful for comparing options, not for budgeting to the last unit.
Reading a health result critically
BMI divides weight by the square of height. It was devised in the nineteenth century to describe populations, not to assess individuals, and it does not distinguish muscle from fat or account for frame size and fat distribution. It systematically misclassifies athletes as overweight, and the standard thresholds were derived largely from European populations, so they fit some ethnic groups poorly.
Calorie and body fat estimates have the same character: they apply an average-case equation to inputs that vary enormously between people. Two people with identical height, weight, age and stated activity level can differ by several hundred calories a day in genuine requirement. Use these figures as a starting point to adjust from, never as a target to hit precisely, and speak to a doctor or dietitian before making significant changes.
Frequently asked questions
Is the financial advice here reliable?
These calculators produce estimates, and nothing on this site is financial advice. They apply standard published formulas to the figures you enter, which makes them genuinely useful for comparing options and understanding how a number is built up. They cannot know your lender's fees, rounding conventions, or your tax circumstances. Confirm anything consequential with your lender, accountant, or a qualified adviser.
Why does each calculator show its formula?
So you can check it. A number with no working behind it is impossible to verify and easy to misread. Showing the formula lets you confirm we have applied the right one for your situation, reproduce the result yourself, and understand what the calculation does and does not account for.
Are the values I enter saved or sent anywhere?
No. Every calculation runs in your browser and nothing is transmitted or stored. This matters more than it might appear, since these inputs are often personal — salary, loan amounts, debts, weight and health measurements. Closing the tab discards everything.
Can I use these calculators for tax filing or official submissions?
No. Use them to understand or estimate a figure, not as the source of a number on a legal or tax document. Tax rules vary by jurisdiction and change over time, and a general calculator cannot account for the specifics of your situation. Check anything official with the relevant authority or your accountant.