How to use this calculator
Select a birth date and a comparison date to calculate completed calendar years, months and days. The comparison date can be today or another date after the birth date. Use the human age mode for ordinary calendar age.
Method and interpretation
Completed years and months are calendar intervals rather than a day count divided by 365. Birthday timing is counted in calendar days so a daylight-saving clock change does not create a fractional age or an extra birthday day.
Assumptions and limits
Month lengths and leap-day birthdays require a calendar convention near month ends. Dog ages and the lifestyle-based biological-age mode are illustrative comparisons, not veterinary or medical measurements. Milestone labels are general examples; legal ages depend on the jurisdiction.
Worked example
A person born on January 15, 2000 is 26 years, 8 months and 16 days old on October 1, 2026. Changing the comparison date to January 15, 2026 gives exactly 26 years with no remaining months or days.