Age Calculator

What this calculator does

Age looks like a subtraction and behaves like a calendar puzzle. Years have uneven months inside them, months have uneven days, and February changes length every four years, which is why mental age arithmetic is wrong so often and why forms that ask for your age in years and months cause so much quiet trouble. This calculator does the calendar properly: exact years, months and days between a birth date and any other date, forwards or backwards, plus the totals underneath it in months, weeks, days, hours, minutes and seconds. It adds the things people actually ask next: the weekday you were born, when your next birthday falls and how many days away it is, the dates of your milestone birthdays, and how many February 29ths you have lived through. The second mode compares two people: who is older, by exactly how much, and how old each of them is on any date you choose, which is the school admissions, sibling gap and eligibility question in one place.

How to use it

1. Age on a date is the main mode. Birth date first, then the date to test. Today is the usual choice, and the button fills it in, but any date works: the age you were when something happened, or the age you will be when something is planned. That second use, checking a future date against a rule such as "must be 18 on 1 September", is where exact days matter more than whole years.
2. February 29 birthdays follow a stated convention. In a year with no February 29, this site observes the birthday on March 1. Some countries and some official forms use February 28 instead. The convention is declared here and in the results so there is never a silent off-by-one; if an official process decides your legal birthday differently, their rule wins for that process, and the limitation section says so plainly.
3. The totals are exact, not estimated. Total days is a true count of calendar days between the two midnights, leap days included. Hours, minutes and seconds are that count multiplied out, which is why they are exact too: 13,300 days is 319,200 hours however you slice it.
4. Age difference mode names the older person. Enter the two birth dates in any order; the calculator works out which is earlier, gives the gap in years, months and days and in total days, and then gives each person's own age on the comparison date, because the gap and the two ages are three different numbers people routinely confuse.
5. Zodiac and generation are labelled informal, on purpose. They are the fun extras people expect on an age page, shown with their nature stated, never dressed up as analysis. The serious numbers on the page are the calendar ones.

How it is calculated

Whole years are counted first: the number of birthdays (using the effective birthday for that year, March 1 for a February 29 birth in a non-leap year) that fall on or before the target date. Whole months are then counted from that last birthday, stepping month by month and clamping the day to the length of shorter months, and the remaining days are a true calendar day count. Total days are computed independently as the exact number of days between the two dates using calendar serial numbers, so the two routes cross-check each other. Nothing is approximated as 365 days a year or 30 days a month anywhere in the page.

Worked examples

A standard case: born Tuesday 15 May 1990, checked on 13 October 2026. The age is 36 years, 4 months, 28 days: 436 complete months, exactly 13,300 days (a satisfyingly round 1,900 weeks), 319,200 hours and 1,149,120,000 seconds. Nine February 29ths fall inside that span. The next birthday is Saturday 15 May 2027, 214 days away, turning 37.

A leap-day case: born 29 February 2000, checked on 28 February 2026. Because the 2026 birthday is observed on March 1 under this site's convention, it has not happened yet on February 28: the age is 25 years, 11 months, 27 days, and the next birthday is the next day, Sunday 1 March 2026, turning 26. Checked on March 1 itself, the age reads exactly 26 years, 0 months, 0 days. This is the case that breaks naive calculators, and the convention is the entire answer to it.

Two siblings: born 15 May 1990 and 20 September 1995. The gap is 5 years, 4 months, 5 days, 1,954 days in total. On 13 October 2026 they are 36 years, 4 months, 28 days and 31 years, 0 months, 23 days respectively: note how the gap in years (5) and the difference between their current ages in years (36 minus 31, also 5) agree here only because both have had their birthdays this year, which is not always so.

Reading your result

If an official form disagrees with this page by a day, the cause is almost always one of three things: a February 29 convention (theirs may be February 28), a form that counts the birth day itself as day one, or a rule written as "age at last birthday" versus "age at next birthday" for insurance purposes, which can shift a quoted age by a full year. The totals give you the evidence to have that conversation precisely: total days is the figure nobody can argue with, because it is a count, not a convention.

Limitations

• Dates, not times. The calculation runs from midnight to midnight on the dates given. Someone born at 11 PM is not a full day old the next morning in hours, but their calendar age advances on the date, which is how every official system counts it too.
• Legal birthdays can differ from this convention. For February 29 births, jurisdictions and individual processes vary between February 28 and March 1. This page uses March 1 and says so; a passport office, insurer or school applying a different rule is not wrong, just different, and their rule governs their process.
• Generation ranges are conventions, not boundaries. The year bands shown are the commonly published ones; sources differ by a year or two at the edges, which is why the label says approximate.
• It cannot verify a date of birth. The arithmetic is exact on the dates entered. A mistyped year produces an exact, wrong answer, so check the weekday of birth line against what you know: it catches more typos than any other line on the page.

Frequently asked questions

Why is my age in months not just my years times 12?

It is, plus the whole months since your last birthday, which is exactly what this page counts. Where people go wrong is counting a month as complete before its anniversary day arrives: born on the 20th, you complete a month on each 20th, not on each 1st. The stepping method used here handles the awkward cases, such as a 31st birth date stepping through February, by clamping to the month's last day.

How many days old am I, exactly?

That is the Total days line, and it is a pure count of midnights crossed since your birth date, leap days included. It is the figure behind the round-number celebrations, the 10,000th day being the popular one: your milestone table and a little arithmetic will find yours.

What is my age on a specific past date, like when I started school?

Put that date in the second box instead of today. The same exact arithmetic runs backwards to any date after the birth, which is how "how old was I when" questions get answered precisely rather than by subtracting years and hoping the months line up.

Does the calculator work for dates before 1900 or far in the future?

Yes. The calendar arithmetic is general, and the milestone table runs to the 100th birthday. Very old dates use the modern Gregorian calendar projected backwards, which is the standard convention for such calculations.

Related calculators

• All Everyday and Time Calculators
• Time Calculator
• Date Calculator
• Playback Speed Calculator
• Reading and Speaking Time Calculator

Method: calendar arithmetic in whole years (effective birthdays, March 1 convention for February 29 births in non-leap years), whole months stepped with day clamping, and exact calendar day counts for all totals; no year or month is ever approximated. Last reviewed: 13 October 2026.