Age Calculator

How an exact age is actually calculated

A correct age is not (today minus birthday) divided by 365.25. That shortcut drifts by a day or more around leap years and birthdays. The right method is calendar subtraction: subtract the years, then the months, then the days, borrowing when a field goes negative — exactly the way you'd subtract one date from another on paper. If the current day-of-month is earlier than your birth day-of-month, you borrow a month and add that month's real length (28, 29, 30 or 31 days), then carry on. This is why someone born on 30 November is '0 months and 19 days' past their birthday on 19 June, not 'about 0.6 months'.

The years figure is the one almost everyone agrees on, because it's what the law uses: your age in years increments on your birthday and not a second before. Months and days are where calculators disagree — borrowing from a 28-day February versus a 31-day January changes the day count by up to three. SnapToolz borrows the length of the month you actually pass through, which matches how a human counts on a calendar.

Age in days, weeks and the leap-year gotcha

• Total days lived is an absolute count — it ignores months entirely and just measures the gap between two dates, so it's immune to the borrowing rules above and is the value to trust for 'how many days old am I'.
• Weeks are simply total days divided by 7; the remainder is the extra days, which is why your 'weeks old' rarely lands on a whole number.
• Leap days matter: anyone alive across 29 February 2024 (or 2020, 2016) has one extra calendar day in their lifetime than the naive times-365 estimate predicts. Over 40 years that's roughly 10 leap days — about a week and a half the back-of-envelope math silently loses.
• A 29 February birthday (a 'leapling') has no birthday in common years. Most jurisdictions and most software treat the legal birthday as 1 March in non-leap years; some treat it as 28 February. The convention is a choice, not a fact — check which one a given system uses before relying on it for anything official.

Timezones, birthdays, and what this tool isn't

Age is computed from calendar dates, not instants in time, so it is deliberately timezone-naive: your birthday is the same date everywhere on Earth, even though the clock moment it began differs by up to 26 hours across zones. The only place a timezone can bite is the definition of 'today' — if you open this near midnight, your device's local date is what's used, so a traveller who has crossed the date line might see 'today' tick over a day before or after the people back home. Compare specific clock times across regions with the World Clock instead.

This is a calculator, not a legal or medical instrument. It will not tell you a gestational age, a 'corrected age' for a premature baby, or the exact age cut-off a school, visa or pension scheme uses — those follow their own rounding rules (often 'age last birthday' or 'age as of 1 September'). For counting a plain span between two arbitrary dates — a notice period, a warranty, a project deadline — reach for Date Difference, which is built for that and exposes inclusive-versus-exclusive counting.