Free online calculators that respect your privacy

What you can work out here

Two calculators, both finished, both maintained. Each one is a full page of tools rather than a single input box, and each explains its own method underneath the result so you can check the work rather than trust it.

Age Calculator

The Age Calculator takes a date of birth and returns an exact age in completed years, months and days — the way birthdays actually work, counting whole calendar years first, then whole remaining months, then the leftover days against the real length of that month.

• The Total card restates the same span as running counts: total months, total days, total hours, total minutes, with weeks available as a toggle in Settings. These are separate answers to separate questions, not conversions of one another.
• Next birthday in counts down to your next birthday and names the weekday it falls on. Leave the live setting on and it ticks against your system clock, once a second.
• Age difference is a second mode on the same page. Give it two dates of birth and it returns the gap in years, months and days, the total days between the two births, and a badge marking who is older.
• Calculate age on sits under More options and accepts any past or future date, with one-tap presets for today and for your next birthday. This is how you answer "how old was I when we moved" or "how old will I be at the wedding".
• Born on reports the weekday you were born plus three cultural labels — western zodiac sign, Chinese zodiac animal, birthstone — which the guide on that page is candid about, because different traditions genuinely disagree.
• Milestones and Fun facts point at the next round numbers ahead of you and at some rough lifetime arithmetic, clearly labelled as estimates from population averages.

Add an optional time of birth and the hour and minute totals stop being counted from midnight and become exact.

BMI Calculator

The BMI Calculator turns height and weight into a Body Mass Index and the small family of figures derived from it.

• BMI and its category, using the World Health Organization adult bands, shown against a scale rather than as a bare number.
• BMI Prime — your BMI divided by 25, so 0.97 reads as "97% of the top of the healthy range". Because it is a ratio, it means the same thing at every height.
• Your healthy weight range for your height: the formula run backwards, giving the weights that correspond to a BMI between 18.5 and 25. If you sit outside it, the page also prints the gap in the unit you entered.
• Waist-to-height ratio, if you add an optional waist measurement. BMI knows your total mass and nothing about where it sits; this second number is the one that distinguishes two people at the same BMI.

Height goes in as feet and inches or centimetres, weight as kilograms, pounds or stone, waist as centimetres or inches. The unit buttons sit beside each field and your choice is remembered. The name, age and gender fields are optional and deliberately inert — they label saved results and never touch the arithmetic.

Worked examples

Ananya needs her exact age for a form

A visa application asks for age in years, months and days as at the date of submission. Ananya was born on 15 May 2000 and is submitting on 21 August 2026.

She opens the Age Calculator, picks 15 May 2000 as the date of birth, expands More options, and sets Calculate age on to 21 August 2026. The hero card reads 26 years, 3 months, 6 days. The Total card underneath gives the same span as 9,594 days, which is the figure most forms want when they ask for days rather than a breakdown.

Had she left the "calculate age on" field alone, it would have used today's date from her device — which is the right default for almost everything except a form dated in advance.

Ravi and Meera settle a five-year argument

Ravi was born 2 November 1994; his sister Meera on 19 July 1999. He has been claiming five years for two decades.

Switch the tab at the top of the form from Your age to Age difference, enter both dates, and the answer is 4 years, 8 months, 17 days — 1,720 days in total. Names are optional; adding them just labels the two rows.

The useful property here is that this gap never changes. It was 1,720 days the day Meera was born and it will be 1,720 days on their eightieth birthdays, which is exactly why "he's five years older" was never going to survive contact with a calculator.

Sam checks a BMI without converting anything

Sam is 5 ft 9 in and 165 lb, and has no interest in doing metric conversion by hand.

On the BMI Calculator he leaves the height unit on FT, types 5 and 9 into the two boxes, sets the weight unit to LB, and enters 165. The result is BMI 24.4, Normal, with a BMI Prime of 0.97 — just under the ceiling of the healthy band. Below it, the healthy weight range for his height reads 125.3–169.3 lb, so he has about four pounds of headroom before the label changes.

Nothing was converted twice and nothing was rounded on the way. The page converts to metric once, divides, and converts the range back into pounds for display.

Why the arithmetic is worth caring about

Three shortcuts account for most of the wrong answers on calculator sites, and all three are invisible unless you check.

Dividing days by 365.25. On 15 May 2026, someone born on 15 May 2000 is exactly 26. That span is 9,496 days; divided by 365.25 it comes to 25.9986, which truncates to 25. A calculator built that way tells people they are 25 on the morning of their 26th birthday. Counting calendar boundaries instead of averaging them removes the problem rather than shrinking it.

Treating a month as 30 days. 15 May to 15 August is 92 days. December to March is 90 days in an ordinary year and 91 when a 29 February lands inside it. There is no fixed number to divide by, so we never divide.

Rounded conversion constants. Swap the exact pound — 0.45359237 kg — for the familiar 2.2 lb per kilogram, and 169.1 lb becomes 76.9 kg instead of 76.7 kg. At 5 ft 9 in that is the difference between a BMI of 24.97 and one of 25.02: the same body, two sides of a category boundary.

What we do not do

There is no account, no login and no email capture anywhere on this site. Nothing you type is uploaded, because there is no server to upload it to — the calculators are static files and the arithmetic runs in your browser. We run no analytics: no page-view tracking, no tag manager, no heatmaps. We set no cookies of our own. There is no newsletter, no premium tier and nothing to buy.

What does exist is optional History, which writes your recent results to your own browser's local storage, capped at 20 entries per calculator, switchable off and clearable in one tap from Settings. It never syncs anywhere.

The site carries advertising, and that is what keeps it free. Being straight about it: serving ads means Google and its partners may set cookies or similar identifiers in your browser to select and measure what you see. Our own pages still set none, and no calculator input is ever passed to an ad network — the ads sit on the page, they do not read it. The Privacy Policy and the Cookie Policy set out what those third parties collect and how to opt out.

Reading a result responsibly

These calculators produce general information, not advice. A BMI is a screening measure — it flags who might benefit from a proper look, and it cannot diagnose anything; it reads high for muscular people and is interpreted against percentile charts, not fixed bands, for anyone under 20. Take the number to a clinician rather than acting on the colour of a bar.

An age result is honest calendar arithmetic, which is not always the same thing as the age an institution will use. Insurers commonly price on age nearest birthday, school systems work from date-based cut-offs, and pension ages are phased by birth date rather than by a clean threshold. Get the true figure here, then check the rule that applies to you.

The full position is in our Terms of Service, and if you think a result is wrong we would rather hear about it than not — the Contact page says what to send.