How age is calculated from a date of birth: years, months, days and Hijri age

The rule your birthday already follows

Everyone agrees on what a year of age is: it passes on your birthday, when the calendar reaches the same day and month as the day you were born. Working out an exact age is that rule applied three times. Count the whole years first, then the whole months since the last birthday, then the days since the last month-day. That is what our Age Calculator does, with the same date code as the site’s other date tools.

Take someone born on 15 March 1994, and ask their age on 3 November 2026.

1. Years. 15 March 2026 has passed, 15 March 2027 has not, so 32 whole years.
2. Months. From 15 March 2026, the 15th of each month follows: April, May, and so on to 15 October. That is 7 whole months, since 15 November is still ahead.
3. Days. From 15 October to 3 November is 19 days.

The answer is 32 years, 7 months and 19 days. The calculator also gives the total, 11,921 days, the weekday of birth (a Tuesday) and the days left to the next birthday: 132, to the 33rd on 15 March 2027.

Notice the order. If you counted days first, or counted months from the end date backwards, you could land on a different split of months and days, since months are not all the same length. Counting forward from the birth date, years, then months, then days, is how a birthday is counted, and it is the order the calculator uses.

When the month is too short: the 31st and 29 February

A birth date on the 29th, 30th or 31st meets months that do not have that day. The calculator’s rule: when the day does not exist in a month, the last day of that month counts instead.

Someone born on 31 January 2008 is, on 28 February 2026, exactly 18 years, 1 month and 0 days old. February 2026 has no 31st, so the month-day falls on the 28th, the month’s last day. The next month-day after that is 31 March again, because the count always goes back to the birth date’s own day rather than drifting to the 28th for good.

Leap-day birthdays follow the same rule. Someone born on 29 February 2000 turns 25 on 28 February 2025, and on 1 March 2025 is 25 years, 0 months and 1 day old. In a leap year the birthday is the 29th again. If a form or a law you are dealing with sets a different rule for leap-day birthdays, follow that rule: the calculator shows the common one.

Your age on a set date

Exam notices, visa forms and job advertisements with an age limit often ask your age on a particular day, not today. The Age on box is for that. It starts at today’s date; change it to the cut-off date printed in the notice and the whole result follows, years, months and days included.

The same box answers questions about the past and the future: how old you were on your wedding day, or how old a child will be on the first day of school. A cut-off can turn on a single day, so type the date exactly as the notice gives it.

The age gap between two people

People often want the difference between two birth dates, for siblings, a couple or a parent and child. Put the older person’s birth date in Date of birth and the younger person’s birth date in Age on. The result is the gap, counted the same way.

For birth dates of 20 August 1986 and 2 April 1991 the gap is 4 years, 7 months and 13 days, or 1,686 days. For a gap in days alone, Days Between Dates gives the count, with the option to include the last day.

Your age in the Hijri calendar

The Hijri year has 12 lunar months, 354 or 355 days in all, about 11 days shorter than the Gregorian year. Count the same life in Hijri years and you get a higher number, and the gap grows by roughly one year every 33 years.

The calculator works out the Hijri age the way it does the Gregorian one. It converts both dates to the Umm al-Qura calendar, the official calendar of Saudi Arabia, using the calendar built into your browser. It counts the whole Hijri years, then the whole Hijri months, and a month only counts once its day of the month has been reached.

Born	Age on 3 November 2026	Hijri age	Hijri date of birth
15 March 1994	32 years, 7 months	33 years, 7 months	2 Shawwal 1414
1 June 1990	36 years, 5 months	37 years, 6 months	7 Dhu al-Qiʻdah 1410
1 January 1960	66 years, 10 months	68 years, 10 months	2 Rajab 1379

The person born in 1960 counts two more years in the Hijri calendar than in the Gregorian one. For a Saudi form that asks for the Hijri date of birth, use the date on your documents; the Hijri Date Converter turns a Gregorian date into its Umm al-Qura date and back.

Two limits are worth knowing. Umm al-Qura is a calculated calendar, and a country that starts its months by sighting the moon can be a day apart from it, so a Hijri birth date recorded by sighting may differ by a day. And the published Umm al-Qura tables run from 1356 to 1500 AH, about 1937 to 2077, so no Hijri age is shown for dates outside that span.

In Excel or Google Sheets

Most of Google’s suggestions for “how to calculate age” are about Excel, and the answer there is a function called DATEDIF. Microsoft documents it as DATEDIF(start_date,end_date,unit), where unit “Y” gives “the number of complete years in the period”, “M” complete months and “D” days. Google Sheets has a DATEDIF function with the same units.

With the birth date in A2, =DATEDIF(A2,TODAY(),"Y") gives the age in whole years, and =DATEDIF(A2,TODAY(),"YM") the whole months since the last birthday. For a fixed date, put that date in another cell and use it in place of TODAY().

For the days, be careful. The unit that should give the days after the last month-day, “MD”, carries a warning in Microsoft’s own documentation: “We don’t recommend using the “MD” argument, as there are known limitations with it.” If you need exact years, months and days for a handful of people, the calculator is quicker and gives the same count as the years-then-months-then-days rule above.

Common questions about the count

Why does a date-of-birth calculator on another site differ by a day? It may count from the end date backwards, or treat every month as 30 days, and either gives a different split of months and days. Test it on a simple case: born on 31 January, age on 28 February. With the rule here that is exactly 1 month.

Does the time of birth matter? Not for age in days, months or years. A person born at 23:50 is one day old the next day, like everyone else born that day.

Does it use my time zone? “Today” in the Age on box is today’s date on your device, which is what matters for a birthday where you live.