Calculate your age from your date of birth and a comparison date. The tool shows your calendar age in years, months and days, plus total days, whole weeks and date-based hours. It also finds the weekday you were born and the days until your next birthday. Today is filled in using your device's local date, and you can change it for a past or future calculation. Dates are processed in your browser. Read the method below if your birthday falls on February 29 or near the end of a month.
Worked example
| Example input or result | Value |
|---|---|
| Birth date | 06/15/2000 |
| Comparison date | 09/20/2025 |
| Calendar age | 25 years, 3 months, 5 days |
| Elapsed calendar days | 9,228 |
| Date-based hours | 221,472 |
How it works
The calculator finds the last completed birthday, then counts completed calendar months from that anniversary. Remaining days are the difference between the final monthly anchor and your comparison date. If the original day does not exist in an anniversary or target month, this tool uses that month's last day. February 29 therefore uses February 28 in a non-leap year. This is our stated calendar convention, not a legal age rule.
Age = completed years + completed months + remaining days
Total days = Julian day number(end) - Julian day number(start)
Whole weeks = floor(total days / 7); hours = total days * 24
Day counts follow the Naval Observatory Gregorian-to-Julian-day algorithm. The Gregorian leap-year rule supplies month lengths. NIST describes the 24-hour day; these hours are date-based conversions, without a birth time.
Read the results
Calendar age and total days describe the same interval in different ways. Years and months follow anniversaries; total days counts the actual date boundaries crossed. The whole-weeks result includes any leftover days. The next-birthday countdown starts from the comparison date, rather than always starting from today.
The worked example uses illustrative date inputs and the same documented formula as the live tool. It is not a statistic about a person. For retirement rules, use the separate SSA table tool instead of treating a general calendar age as a benefit decision.
Frequently asked questions
How do I calculate my age from my date of birth?
Enter your birth date and the date you want to compare it with. The result shows completed years, months and remaining days, followed by total days and date-based hours.
Can I calculate my age in months and days?
Yes. The main result breaks the interval into completed years, months and days. Multiply the completed years by twelve and add the displayed months for completed calendar months under this tool's convention.
How do I find my age on a specific date?
Change the comparison date above or use the age-on-a-date tool. The comparison date can be in the past or future, but cannot be earlier than the birth date.
How many days or hours old am I?
Total days is the elapsed calendar-date difference. Date-based hours multiply that count by twenty-four. These hours do not include the time of birth, the current time of day or daylight saving changes.
Does this age calculator handle leap years?
Yes. It follows the Gregorian rule supplied by the U.S. Naval Observatory. February 29 births use February 28 as their anniversary when the comparison year has no February 29.
How do I calculate my next birthday?
The tool finds the next anniversary on or after the comparison date. If that date is your birthday, the countdown is zero. The weekday result refers to your original birth date.