Age Calculator: Years, Months, Days & Next Birthday
Calculate calendar age between a date of birth and a chosen date. See years, months, days, total elapsed days, and the next birthday using local calculations.
✓ Processed on your deviceYour result
Calculate age on any supported calendar date
The tool measures calendar years, remaining months, and remaining days. The comparison date defaults to your device’s current date and can be changed. Dates are treated as calendar days, so time zones and daylight-saving changes do not add or remove hours.
How calendar age is counted
The calculator advances by whole months from the birth date, clamping to the last valid day when the target month is shorter. It then counts remaining calendar days. Twelve whole months make one year.
Calendar age = whole clamped months, split into years and months, plus remaining days.
Total days = comparison date − birth date, measured in calendar days.
Leap-day birthdays
A February 29 anniversary is treated as February 28 in non-leap years. This is an explicit calculator convention; legal or administrative age rules may differ. For example, a birth date of 2000-02-29 gives 23 years on 2023-02-28 under this convention.
Limits
Dates from year 0001 to 9999 use the proleptic Gregorian calendar. Historical local calendar changes are not modeled. The result does not establish legal eligibility, medical milestones, or identity.
Calendar reference: US Naval Observatory: Gregorian leap years.
About this tool
Prepared by the UtilitiesWeb team at The Alpha 1 Company. Review results before using or sharing them.
Methodology updated: 1 November 2026. Inputs are processed locally; clearing or leaving the page releases the working result.