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Every date question, answered.

Eight fast, precise date calculators — from your exact age to a due date, a countdown, or the working days between two dates.

Age CalculatorYour exact age to the day, plus a live second-by-second ticker.Date DifferenceThe precise gap between any two dates.Day of the WeekWhat day of the week any past or future date falls on.Countdown TimerA live, shareable countdown to any event you care about.Business DaysWorking days between dates, minus weekends and public holidays.Time Zone ConverterCompare the current time across cities around the world.Historical AgeHow old was someone when history was made?Pregnancy CalculatorDue date, current week, trimester and weekly milestones.

Which calculator do you need?

Most date questions look alike and are not. “How long is it until March?” and “how many working days is it until March?” differ by roughly a third, and “three months” and “ninety days” are almost never the same date. Start from the question rather than the tool:

How old am I, exactly?Age Calculator
How long between these two dates?Date Difference
How many working days do I actually have?Business Days
What day of the week was — or will be — that?Day of the Week
How long until my event?Countdown Timer
What time is it for the people I'm meeting?Time Zone Converter
When is my baby due, and how far along am I?Pregnancy Calculator
How old were they when they made history?Historical Age

Why exact date arithmetic is harder than it looks

Calendar months run from 28 to 31 days. Years run 365 or 366. Clocks shift by an hour twice a year in about a third of the world, and the dates on which they shift are set by legislation that changes. Any shortcut that treats a month as 30 days or a year as 365.25 will be wrong by a day or more over a realistic span — and “a day or more” is the difference between filing on time and filing late.

Every calculator here counts whole calendar units first — years, then months — and borrows the real length of the preceding month for whatever is left over. That is the same convention used by civil registries, by contract law in most jurisdictions and by the ISO 8601 duration model, and it is why the age this site reports is the one that appears on official forms. Date-only arithmetic is anchored to UTC, so a calendar date means the same thing whether you load the page in Los Angeles or in Auckland.

Where two honest answers exist, we show both rather than picking for you. The date difference calculator reports a span as years-months-days and as flat totals of months, weeks, days and hours, because payroll needs one and a contract needs the other.

Built to run entirely in your browser

There is no server-side component to this site. The calculation engine is a few kilobytes of JavaScript that ships with the page, so the dates you enter are processed on your device and never transmitted anywhere. That is a deliberate design choice, not a limitation: due dates and birth dates are exactly the kind of data that should not sit in someone else's log file. It also means the tools keep working offline once the page is loaded, and that results appear instantly rather than after a round trip.

The same engine is implemented for the free Android app, verified against an identical set of test cases, so a figure you read on your phone matches the one on the web to the day. Read more about how the site is built and who maintains it.

Guides

Longer explanations of the date problems people get wrong most often — written to be read on their own, whether or not you use the tools.

How to calculate your exact age by handThe borrowing method registrars and payroll systems use, why dividing days by 365.25 drifts, and how leap-day birthdays are handled.Business days vs calendar days: what your contract actually means“30 days” and “30 business days” differ by about twelve days. How the two are defined, which one applies by default, and how to plan around both.Pregnancy weeks explained: why 40 weeks starts before conceptionGestational age, fetal age, Naegele's rule and why an estimated due date is a midpoint rather than a deadline.Leap years, the 400-year rule, and the eleven days Britain lostWhy 2000 was a leap year and 1900 was not, how the Gregorian reform worked, and what leap seconds have to do with any of it.How to schedule across time zones without getting it wrongWhy UTC offsets are not fixed, how daylight saving breaks recurring meetings, and a practical method for finding a slot that works.

Frequently asked questions

Are the calculators really free?

Yes. Every tool on the site is free, unlimited and available without an account. There is no premium tier and no feature is held back. The site is paid for by display advertising, which is why you will see clearly labelled ad slots alongside the tools.

Do I need to create an account?

No. There is no sign-up, no login and no newsletter gate. Open a calculator and use it.

Where are my dates sent?

Nowhere. Every calculation runs in your browser using JavaScript that ships with the page. We operate no backend and no database, so the dates you type — birth dates, due dates, countdown targets — never leave your device.

Why do the results differ from a quick subtraction?

Because months and years are not fixed lengths. Our calculators count whole calendar units first and borrow the real length of the preceding month for the remainder, which is the convention used by civil registries, contracts and payroll systems. A day-count divided by 30 or 365.25 will drift by a day or more.

Is there a mobile app?

Yes. Age & Date is also published as a free Android app with the same eight calculators and the same calculation engine, so the numbers match exactly on both.

How accurate are the live counters?

A single one-second timer drives every live value on the site, and each tick recalculates from the current clock rather than decrementing a stored number. That means the counters snap back to the correct value after a background tab has been throttled instead of drifting.