Age Calculator: Exact Age and Age Difference Between Two Dates

The calculator counts full calendar years first, then full calendar months, then remaining days. When the target day falls earlier in the month than the birth day, it counts the remaining days from the most recent monthly anniversary, so the day count never turns negative. This gives the same result you would get by counting anniversaries on a physical calendar. For the worked example of January 1, 2000 to January 1, 2025, this method returns exactly 25 years, 0 months and 0 days, since the target date falls on the same calendar day as the birth date. For a non-anniversary case, such as a birth date of March 15, 1990 checked against October 20, 2025, the same logic returns 35 years, 7 months and 5 days rather than a round number, which is where the breakdown becomes more useful than a single age figure. This calendar-based method mirrors how ages are stated on official documents and payroll records, rather than an average built on a fixed 365.25-day year.

It describes what happens when the target day is smaller than the birth day: the last full month is counted from the most recent monthly anniversary, and the days after it are added. When the birth day does not exist in a month, the last day of that month counts as the anniversary. Born March 31 with a target of May 10, the monthly anniversary in April falls on April 30, so the result is 1 month and 10 days. This prevents a negative day count and keeps the result in line with the calendar.

A calendar month is complete when the same day of the month is reached again. For example, from January 15 to February 15 is exactly one month, regardless of how many days are in January or February. Months are not assumed to be 30 days; the actual calendar is used.

Every February 29 that falls between the birth date and the target date is counted as a regular calendar day in total-day calculations. Over 25 years starting January 1, 2000, there are 7 such leap days, giving 9,132 total days rather than 9,125. Leap years do not affect the year-month-day output unless the birth date itself is February 29. The rule that skips a leap day in most century years, such as 2100, does not apply to the 2000 to 2025 example, since none of those years fall on a skipped century boundary. If the target date lands exactly on February 29, the total-day count still includes that day normally, and the year-month-day breakdown treats it the same as any other calendar date, even though it only recurs once every four years. The skip rule itself has an exception: century years divisible by 400, such as 2000, stay leap years, which is why 2000 still counts among the 7 leap days above despite the century boundary.

February 29 exists only in leap years. In non-leap years the calculator uses February 28 as the birthday, both for the year-month-day breakdown and for the birthday countdown, so someone born on February 29, 2000 turns 1 on February 28, 2001. In leap years February 29 itself is the birthday. For official purposes the legal rule can differ by country, so check the rule that applies to you.

Total weeks equal the total number of calendar days divided by 7. The result is shown as whole weeks plus any remaining days, since a week is exactly 7 days. For example, 9,132 days equals 1,304 weeks and 4 days. Weeks × 7 plus leftover days always sum to the total day count.

Hours equal total days × 24. Minutes equal total hours × 60. Seconds equal total minutes × 60. For the 25-year example (9,132 days): 219,168 hours, 13,150,080 minutes, and 789,004,800 seconds. These values count from midnight on the birth date to midnight on the target date.

The countdown shows how many days remain from the target date until the next occurrence of the birth month and day. If the target date is the birthday itself, the countdown shows 0 days. The countdown is based purely on the calendar date of birth, not the day of the week.

Yes. Enter any future date as the target to calculate a projected age. This is useful for planning: see how old you will be at retirement, check when a child will reach a school eligibility age, or verify an age requirement on a specific future deadline.

A calendar year is 365 or 366 days, not exactly 52 × 7 = 364 days. Over 25 years, 9,132 days gives 1,304 full weeks and 4 extra days, not 1,300 weeks (25 × 52). The extra days accumulate from the difference between 365 days per year and 52 × 7 = 364 days, plus leap days. Even over a single non-leap year the same gap appears on a smaller scale: 365 days equal 52 weeks and 1 day, not an even 52 weeks, which is why your birthday shifts to a different day of the week most years. This also means two people born exactly one calendar year apart are not always precisely 52 weeks apart in total elapsed time, since a leap day between their birth dates adds one extra day to that gap.

Yes. The calculator measures the elapsed time between any two dates, not just birth dates. You can use it to find the age of a company, a contract, a vehicle, a building, or any other event. Just enter the start date as the birth date and the end date as the target date.

The year-month-day breakdown is exact for the dates entered and matches standard calendar conventions used by most official documents. Total-unit figures (weeks, hours, minutes, seconds) are also exact, counting from midnight on each date. The only assumption is that a day runs from midnight to midnight and that no time of birth is entered.

Yes: open the Age difference tab and enter both birth dates, in any order. The calculator shows the gap in years, months and days, the same gap in months, weeks and days, and which of the two people is older. For someone born March 15, 1990 compared with someone born January 1, 2000, the result is 9 years, 9 months and 17 days, or 3,579 days in total. The result does not change when you swap the two dates, only the line that says who is older does. The same tab works for any two dates, not just people, so it is also a quick way to compare the ages of siblings, check the age gap required by some insurance or legal eligibility rules, or measure the interval between two historical events. Two people born on the same day get a gap of 0 years, 0 months and 0 days, and the calculator says so instead of naming an older person.

Enter today's date as the target date to see the countdown to your next birthday displayed just below the main result. For someone born January 1, entering March 1 of the same year shows 306 days remaining until the next birthday. The countdown always points to the next occurrence of your birth month and day, counting into next year if this year's date has already passed. If today happens to fall exactly on your birthday, the countdown shows 0 days, and from the next day on it counts down a full year to the following birthday: 364 days, or 365 when a February 29 falls in between. For someone born on February 29, the countdown uses February 28 as the birthday in non-leap years, so it still reaches zero on a real calendar date even though the exact birth date only recurs once every four years.

Use the DATEDIF function with the birth date in one cell and the end date in another. With the birth date in A1, =DATEDIF(A1,TODAY(),"Y") returns the age in full years, =DATEDIF(A1,TODAY(),"YM") the extra full months, and =DATEDIF(A1,TODAY(),"MD") the remaining days. For a birth date of March 15, 1990 and an end date of October 20, 2025, those three formulas return 35, 7 and 5, the same 35 years, 7 months and 5 days this calculator shows. Microsoft warns that the "MD" unit can return a negative, zero or inaccurate result in some month-end cases, so check the days against a calendar when the birth day is the 29th, 30th or 31st. DATEDIF does not appear in the function list or autocomplete, but typing it in full works in current versions of Excel. For the total number of days, simply subtract the birth date from the end date and format the cell as a number.

No. This age calculator is for informational and planning purposes only. For official age verification (medical eligibility, legal identity, government benefits), always use certified documents such as a birth certificate and consult the relevant authority.