Age Calculator

Your "total months lived" counts every complete calendar month since birth — this equals (years × 12) plus the partial year's complete months. The "age months" field in the breakdown shows only the remaining months beyond complete years. For example, someone who is 25 years and 3 months old has 303 total months lived (25 × 12 + 3).

For Leap Day birthdays (February 29), this calculator uses March 1 as your next birthday in non-leap years — the same standard used in most US legal contexts. Some people choose to celebrate on February 28. For age calculation purposes, you turn a new age at the same moment as everyone else: midnight at the start of your birthday date.

The calculator uses JavaScript's Date object, which implements the Gregorian calendar. By creating a Date from your birth date, it determines the exact day of the week. This is accurate for any date after the Gregorian calendar was adopted (October 15, 1582). Note that dates before September 14, 1752 in the UK and US were under the Julian calendar, which may differ by days from the Gregorian calculation.

Total seconds is calculated from midnight on your birth date to midnight today — it does not account for the actual time you were born. If you were born at 3pm, you've actually lived about 54,000 fewer seconds than the calculator shows on your birthday. For most purposes this level of precision is sufficient, but birth time would be needed for an exact count.

The calculator works with calendar dates only (year, month, day) and ignores clock time entirely. This means daylight saving time transitions — which shift clocks by 1 hour twice a year — do not affect the age or day calculations. Only the total hours, minutes, and seconds figures would be off by a tiny fraction due to DST, which is negligible for any practical purpose.

For Social Security, early retirement benefits can start at exactly age 62, with reduced payments. Full retirement age is 66–67 depending on birth year (67 for those born 1960 or later). Delayed credits accrue up to age 70. For Medicare, enrollment begins at age 65 — you can sign up during a 7-month window around your 65th birthday. Use this calculator to determine when those milestones fall for your specific birth date.