Calculate age on a chosen date

Both dates are civil dates (no time, no time zone). If the arrival date is empty, the engine takes the current date on the server/runtime. Age decomposes as a calendar gap: count years, adjust months, then days from the real length of the previous month. An age “in the future” (birth after the arrival date) is refused. The next birthday is the next occurrence of the birth month and day; born on Feb 29, if the target year is not a leap year, the date kept is Feb 28.

âge = décomposition (naissance → date d’arrivée)

jours calendaires = datearrivée − datenaissance

The calendar is civil Gregorian. Leap years insert Feb 29; typed-date validity is checked (no April 31, no Feb 29, 2026). Age is not converted to “decimal years” (26.2 years): that shortcut ignores month lengths. The next birthday does not slide to March 1: the convention here, for a Feb 29 birth, is Feb 28 in non-leap years.

Date of birth

Date of birth or the start of an “age” (company formation, in-service date). Must be on or before the arrival date.

Age on

Date at which you want the age. Empty = today at calculation time. For a reproducible example, type a fixed date (such as 2026-08-25).

Assumptions

• Gregorian civil dates, no time of day.
• One day = one UTC calendar step, not a 86,400 s duration with daylight saving.
• Born Feb 29: next birthday on Feb 28 if the year is not a leap year.

Limits

• No age “in moons” and no school-year age (birth year as of Dec 31).
• No time zone: midnight in Tokyo and midnight in New York on the same civil day are the same age here.
• Julian, revolutionary, or lunar calendars are not handled.

26 years, 2 months, and 10 days is vital-records age, not HR software that cuts at the year. The 9,567 days help if a text asks “older than n days.” For a lease that counts occupancy days (arrival and departure included), the “days between two dates” tool is clearer than age.

• Dividing the number of days by 365 to get age.

  Leap years and month lengths make that quotient wrong by a day or two, sometimes more. Civil decomposition is the exact age.

• Swapping birth and arrival date.

  A future birth is refused. For any signed gap, use the date-difference tool.

• Believing a Feb 29 birth “only has a birthday every 4 years” in this tool.

  Age advances every year. Only the next-birthday date is placed on Feb 28 in non-leap years.

• Date differenceThe main result is a decomposition: 2 years, 5 months, and 10 days, for example. Total days sit beside it. That is not the same need as “how many stay nights.”
• Days between two datesFrom January 1 to January 3, the exclusive gap is 2, the inclusive count is 3. Both are right; they do not answer the same sentence. This tool shows both, without choosing for you.
• Pregnancy due dateOne date: the first day of the last period. The tool adds 280 days for the due date and 14 days for a model conception.
• Dog ageAge and size. The tool applies a stepped chart, not the “times seven” rule.
• Cat ageAn age in years. The tool applies 15, then 9, then 4 — not “times seven”.

Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.

This calculation uses a standard mathematical identity. See also the methodology.