Enter your date of birth and the tool computes your exact age as years, months and days by walking the calendar month by month, borrowing real month lengths so leap years and short months are handled correctly. It also reports the total number of days and weeks you have lived, the weekday you were born on, and a live countdown to your next birthday. If today is your birthday, the countdown reads zero.
Ages are measured against today in your local time zone, using calendar dates with no time-of-day, so the count never drifts by a day across daylight-saving changes. The next-birthday logic accounts for people born on February 29 by rolling to the following valid day. Everything is calculated locally in your browser and your birth date is never uploaded.