Calculate age for a chosen reference date
Start with the reference date
Enter a birth date and the date on which you want to measure age. The reference defaults to today on your device, but you can choose a past or future date. A birth date later than the reference is rejected. The calculation compares dates; it does not determine a person’s eligibility for a service or legal status.
How years, months and days are separated
The tool finds the largest whole number of calendar months that fits before the reference date, clamping to the last valid day of a shorter month. It then groups 12 months into a year and reports the days remaining. This convention keeps month-end intervals nonnegative.
Leap-day birthdays
Leap days count in calendar totals. The birthday countdown uses March 1 for a February 29 birthday in a non-leap year. The age breakdown uses the month-end clamping convention described above, so its completed-month boundary can differ from the birthday countdown.
What totals mean
Months are completed calendar months; weeks are complete groups of seven calendar days. Hours are a 24-hour-per-day equivalent, because the input has no birth time or birth time zone. They should not be read as an exact count of hours lived.
A reference-date example
| Birth date and reference | Calendar age |
|---|---|
| July 17, 2000 → July 17, 2026 | 26 years, 0 months, 0 days |
| July 17, 2000 → August 20, 2026 | 26 years, 1 month, 3 days |
| January 31, 2026 → March 1, 2026 | 0 years, 1 month, 1 day with month-end clamping |
Frequently asked questions
Is today the same for every visitor?
No. Today comes from the visitor’s device and local date. Use an explicit reference date for a reproducible result.
Does this calculate age in exact hours?
No. Without a birth time and time zone, the hours display is only a calendar-day equivalent.
Can I use it for an application cutoff?
You can calculate age on the stated cutoff date. The organization’s eligibility rules must be checked separately.
See the rules and formulas in our calculation methodology. Found a discrepancy? Send an example for review.
Explanation reviewed October 17, 2026. Example results depend on the stated assumptions.