How calendar age is counted
The calculation counts complete calendar months from the birth date, then the remaining days. Twelve complete months make a year. It uses dates rather than times, so your time zone and a daylight-saving change do not add or remove a day from the difference.
When a month has no matching day
For a January 31 start, a one-month anniversary falls on February’s last day. For February 29, an anniversary in a non-leap year uses February 28. This is the calculator’s convention; rules for legal age or official deadlines may differ.
A worked example
From June 15, 2000 to June 15, 2026 is exactly 26 years. One day earlier is 25 years, 11 months, and 30 days. The total days count includes leap days within the interval.
What the totals mean
Complete weeks are total days divided by seven, rounded down. Hours are total days multiplied by 24; they do not measure the exact elapsed hours between two birth times. No date of birth is sent to a server by this calculator.