Age seems simple until you need it exactly: for a form that asks for age in months, a milestone birthday, an eligibility cutoff, or just curiosity about how many days you have been alive. This calculator gives the calendar age in years, months and days, then the same span in weeks, days, hours and minutes.
How it is calculated
- Years, months and days are counted the way people do: whole years first, then whole months, then the remaining days. A month is complete when the same day of the month comes around again. Someone born January 31 is 28 days old on February 28 and 1 month and 1 day old on March 1, because February has no 31st.
- Total days is the plain difference between the two dates, so leap days are included automatically.
- Weeks, hours and minutes are derived from total days. Months for the "in months" line are years × 12 + months.
- Next birthday is the next occurrence of the birth month and day. People born on February 29 get March 1 in non-leap years. Legal rules vary by country; Hong Kong law, for example, sets March 1.
Example
Born June 15, 1990, checked on September 14, 2026: 36 years, 2 months and 30 days; 13,240 days; about 1,891 weeks. Born on a Friday. Next birthday in 274 days.
Why age in months matters for babies
Pediatric growth charts and vaccine schedules use months, and "18 months" means exactly 18 calendar months from the birth date, not 78 weeks. Enter the birth date and today, and read the "in months" line.
Age on a specific date
Change the second date to answer questions like "how old will I be on the day of the wedding" or "how old was she when the photo was taken". The calculation is the same, just anchored to that date.
Frequently asked questions
How do I calculate my age exactly?
Count whole years from your birthday, then whole months, then the days left over. The calculator does this from the two dates and also shows the total in days, which is the most precise single number.
What is the formula to calculate age?
Subtract the birth year from the current year, then subtract 1 if your birthday has not come yet this year. For months and days, add the whole years to the birth date, count the whole months after that, and count the days left over. The "How your age was counted" block above shows these steps for your dates.
Is there a formula in Excel to calculate age?
Yes. With the birth date in A2, =DATEDIF(A2,TODAY(),"Y") gives complete years and =DATEDIF(A2,TODAY(),"YM") the months after the last birthday. Microsoft does not recommend the "MD" option for the remaining days, because it can return a negative number, a zero or an inaccurate result, so check the days here.
How many days old am I?
Enter your birth date above; total days is shown in the result panel. As a rough check, multiply your age in years by 365.25.
What if I was born on February 29?
In years without a February 29 the calculator uses March 1 as your birthday. Legal rules vary by country; Hong Kong law, for example, sets March 1. Your exact age in days is unaffected.
How is age calculated in months for a baby?
From the birth date, in calendar months: a baby born on the 10th turns one month old on the 10th of the next month. Weeks and months are not interchangeable; 4 weeks is not a month.
Does the calculator account for leap years?
Yes. Total days is the real difference between the dates, and calendar months handle February correctly.
Read more
- How to calculate age from a date of birthThe formula for age in years, months and days, worked through by hand, the cases where it trips people up (the 31st, February 29), the Excel formula and its known flaw, and how Korean age differs.
- How to count days between two dates, and whether to count the first dayThe formula for days between dates, when to add 1 for counting both ends, how deadlines like "within 30 days" are counted in the US and the UK, and a table of common cases from hotel stays to whole years.
Sources
- ISO 8601 date and time format
- Microsoft Support: DATEDIF function
- CDC growth charts: age in months
- Hong Kong Age of Majority (Related Provisions) Ordinance (Cap. 410), section 5: birthdays on February 29
By Calcelate Team. Formula from the sources above.
- 2026-10-14 · Formula and texts checked