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How to Calculate Your Exact Age (Years, Months, Days)

Gizmoop Team · 6 min read · May 23, 2026

To calculate your exact age, subtract your birth date from today and handle the day and month carries. Most people use the rough formula "current year minus birth year", but that is only right for about half the year (after your birthday). The exact age in years, months, and days requires a full date subtraction.

The simple formula (year only)

Age in years = current year - birth year - (1 if birthday has not occurred this year, else 0).

Example: born June 15, 1990. Today is May 23, 2026. June 15 has not happened yet in 2026, so age = 2026 - 1990 - 1 = 35. On June 15, 2026, age becomes 36.

This works for filling out forms ("age 35") but loses the months and days.

The exact formula (years, months, days)

Step 1: Subtract birth day from today's day.

Step 2: If the result is negative, add the number of days in the previous month, then subtract 1 from the month count.

Step 3: Subtract birth month from today's month (after any adjustment from step 2).

Step 4: If the result is negative, add 12 to the months and subtract 1 from the year count.

Step 5: Subtract birth year from today's year (after any adjustment from step 4).

Result: years, months, days.

Worked example

Birth date: June 15, 1990. Today: May 23, 2026.

  1. Today's day (23) - birth day (15) = 8 days. Positive, no carry needed.
  2. Today's month (5) - birth month (6) = -1. Negative. Add 12 and subtract 1 from years: months = 11, year carry = -1.
  3. Today's year (2026) - birth year (1990) - 1 (carry) = 35.
  4. Result: 35 years, 11 months, 8 days.

Sanity check: 35 years 11 months 8 days from June 15, 1990 lands on May 23, 2026. Correct.

The Excel/Google Sheets way

Use the DATEDIF function. The syntax DATEDIF(start_date, end_date, unit) returns the difference in the specified unit:

  • =DATEDIF(A1, TODAY(), "y") returns whole years.
  • =DATEDIF(A1, TODAY(), "ym") returns leftover months after the whole years.
  • =DATEDIF(A1, TODAY(), "md") returns leftover days after the whole years and months.

Combine in one cell: =DATEDIF(A1,TODAY(),"y")&" years, "&DATEDIF(A1,TODAY(),"ym")&" months, "&DATEDIF(A1,TODAY(),"md")&" days" produces "35 years, 11 months, 8 days".

Age in days, hours, minutes, seconds

Subtract the two dates in milliseconds (JavaScript) or days (Excel) and convert.

  • Days: (today - birth date) divided by milliseconds in a day (86,400,000).
  • Hours: days × 24.
  • Minutes: hours × 60.
  • Seconds: minutes × 60.

So a 35-year-old has lived about 12,783 days, or 306,800 hours, or 18.4 million minutes, or 1.1 billion seconds. These are fun figures but rarely useful for official purposes.

Common edge cases

February 29 birthdays. Born on Feb 29? In non-leap years, the convention is to celebrate either Feb 28 or Mar 1, depending on culture and personal preference. Most calculators (including ours) treat Feb 28 as the anniversary date for legal age in non-leap years.

Born across time zones. A baby born at 11pm Pacific time on January 1 is technically born on January 2 in Eastern time. Birth certificates use the local time of birth. Age calculators using your computer's local time may show a date one off if your timezone differs from your birth timezone.

Daylight saving time. The shift from standard to daylight saving (or back) can briefly shift the day boundary near midnight. This rarely affects calculated age because the calculation rounds to whole days.

How software handles it

JavaScript's built-in Date object handles all the leap year, month length, and time zone arithmetic correctly. Our age calculator uses the Date object. The same calculation in Excel uses DATEDIF, which is identical in approach. Python uses the datetime module with similar logic. Most age calculators across languages converge on the same answer because they all rely on the same underlying date arithmetic.

The 1 percent of cases where calculators disagree: leap-year Feb 29 birthdays in non-leap years, and edge cases right around midnight in different time zones. For all other dates, every reasonable calculator gives the same year-month-day breakdown.

Use our age calculator

Type your birth date into our age calculator and see your age in years/months/days, total days, total weeks, total hours, total minutes, total seconds, plus when your next birthday is. The calculator runs in your browser, so no data is uploaded. It handles all the edge cases correctly.

Frequently asked questions

Subtract the birth date from today, handling carries. Start with days: if today's day is less than the birth day, borrow days from the previous month and subtract one from the month count. Then months: if today's month is less than the birth month, borrow 12 months from the year and subtract one year. The result is years, months, days. Our age calculator does this instantly.

Age in years = current year minus birth year, then subtract 1 if your birthday has not happened yet this year. So someone born in 1990 in October is 35 from January 2026 to September 2026, then 36 from October 2026 onward (assuming no birthday yet). Year-only age is approximate; for the exact age, use the full day-month-year calculation.

Leap years matter only for February 29 birthdays. In non-leap years, the "anniversary" is usually celebrated on February 28 or March 1, depending on personal preference. The exact-age calculation in our calculator treats Feb 29 birthdays correctly: someone born Feb 29, 2000 is exactly 25 years and 0 days old on Feb 28, 2025 (one day before age 25 turns 26 a year later in the leap year of 2028 some calculators round differently). Most software treats Feb 28 as the anniversary in non-leap years.

For Excel: =DATEDIF(birth_date, TODAY(), "y") gives years. =DATEDIF(birth_date, TODAY(), "ym") gives leftover months. =DATEDIF(birth_date, TODAY(), "md") gives leftover days. Combine these to get years, months, days. Google Sheets has the same DATEDIF function with the same syntax.

Standard age calculators are accurate to the day. They use the browser's Date object which handles leap years, month lengths, and date arithmetic correctly. Edge cases (Feb 29 birthdays, time zone boundaries) may differ by a day between calculators because of rounding choices, but the year and month values are universally consistent.

Yes. Subtract the two dates and divide. Days = (today - birth date) / 86,400,000 milliseconds. Hours = days × 24. Minutes = hours × 60. Seconds = minutes × 60. So a 30-year-old has lived about 10,957 days, 263,000 hours, or 947 million seconds. Our age calculator displays these alongside the years-months-days view.

Legal age is reached at midnight on your birthday. So someone born June 15, 2008 turns 18 at midnight on June 15, 2026. For exact ages used in contract law, the convention is that age is reached at the start of the birthday in the relevant time zone, not at the exact hour of birth.

Three common causes. Time zone differences: if your birth time zone differs from your current time zone, the date arithmetic can be off by 24 hours. Daylight saving: leaping forward an hour can shift date boundaries near midnight. Leap year edge cases: Feb 29 birthdays in non-leap years require a convention choice (Feb 28 or Mar 1) that differs across calculators.

You can estimate within one year of accuracy. If you know just the birth year, the person is either (current year - birth year) or (current year - birth year - 1), depending on whether their birthday has already happened this year. Without the birth month and day, you cannot get a more precise figure.