Find your birth date from your age, plus star sign and zodiac
Ever wondered what day of the week you were born on, or what your Chinese zodiac animal is? The date of birth calculator takes your age and works backwards to estimate the date you were born, then reveals fun facts about that date including the day of the week, your Western star sign, your Chinese zodiac animal, and exactly how many days you have been alive. This calculator is useful for more than just curiosity. Age verification forms sometimes require a date of birth, and if you only know someone's approximate age, this tool helps estimate the date. Parents might use it to calculate a child's birth date from their age for school enrolment forms. It is also a popular party trick: tell someone your age and they can tell you what day of the week you were born. The calculator uses calendar arithmetic to subtract years, months, and days from a reference date (today by default). It accounts for varying month lengths and provides the most likely date of birth based on the age information you provide. For greater precision, include months and days alongside the year.
To use the date of birth calculator: 1. Enter your age in years. This is the primary input and is required. If you only know the number of years, leave months and days at zero. 2. Optionally enter additional months and days for a more precise result. For example, if you are "25 years and 6 months old," enter 25 in years and 6 in months. 3. The reference date defaults to today. If you want to calculate from a specific date (for instance, finding what date of birth corresponds to being 30 years old on a particular day), change the reference date to that specific date in YYYY-MM-DD format. 4. View the results: your estimated date of birth, the day of the week you were born, your Western star sign, your Chinese zodiac animal, and the total number of days you have been alive. 5. Note that the calculation is an estimate. Because months have different numbers of days (28 to 31) and leap years add an extra day in February, the result may vary by a day or two in edge cases.
The calculation works by subtracting the age components from the reference date: Step 1: Start with the reference date (today or a specified date) Step 2: Subtract the number of years Step 3: Subtract the number of months Step 4: Subtract the number of days Example: If you are 30 years old on 26 March 2026, the calculator subtracts 30 years from 2026-03-26 to get 1996-03-26. This was a Tuesday, and falls under the Aries star sign (21 March to 19 April). The year 1996 in the Chinese zodiac is the Year of the Rat. Star signs are determined by the month and day of the estimated birth date, following the standard Western zodiac date ranges. The Chinese zodiac follows a 12-year cycle based on the birth year: Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, and Pig. Days alive is calculated as the number of full days between the estimated date of birth and the reference date. This accounts for leap years automatically through standard date arithmetic.
Fun facts about birth dates: approximately one in 365 people share your exact birthday, which means in a group of just 23 people there is a 50% chance that two share the same birthday (the "birthday paradox"). The most common birth month in the UK is September, with the least common being February. If you were born on 29 February (a leap year baby), your actual birthday only comes around every four years. For calculating the exact number of days between two dates, try our Date Difference Calculator. To find your current age from a known date of birth, use our Age Calculator.