Age Calculator

The Age Calculator tool converts a birth date to the exact age. After entering the birth date it calculates the number of years, months and days until today or any selected date while showing the total time spent in weeks, days, hours, minutes and seconds. The panel is updated in real-time as you type.

How to use the age calculator:

Leave the mode set to "How old am I?", enter your date of birth and check the age shown on the right. By default it calculates the age based on today's date. To find out how old you were at a different date - for example, for an upcoming birthday, a past milestone or documented age - change the reference day to "Specific Date" then select the desired date.

The second mode "When was I born?" does the calculation backwards. If you enter a known age and the date on which that person had that age, then the tool calculates the birthdate backwards. This is useful for genealogical research because census records or tombstones often list an age rather than a birthdate.

How age is calculated:

Age is the time difference between two dates and is calculated in a manner consistent with how age is commonly expressed. A person does not become one year older until their first birthday and never "rolls over" to an earlier day. The tool will first calculate the number of full years between the two dates, then the number of full months from the remainder, and finally the remaining days.

Suppose a person was born on November 15, 2006 and we want to calculate their age as of March 10, 2026. We line up the two dates side by side and start subtracting from right to left. Since the number of days is negative, we borrow one month. February 2026 has 28 days so: 10 + 28 = 38, and 38 - 15 = 23 days. From the months we borrow a year. 2 + 12 = 14, and 14 - 11 = 3 months. Finally: 2025 - 2006 = 19 years. So their age is 19 years, 3 months, and 23 days.

The calculators count the date of birth as day zero and counting begins only after a full 24 hours have passed. So someone born on March 15 will be one day old on March 16. This is how age is calculated in hospitals, spreadsheets, and legal documents.

Displaying age in all units

As newborns are measured in days or weeks, toddlers in months and everyone else in years, the calculator displays all units simultaneously. In addition to "age in years, months and days" view, it also shows total elapsed months, weeks and days as well as a decimal age that can be used in tables where a decimal age is required.

The "Total Age" chart converts your entire life into a single selected unit. By switching to hours, minutes and seconds you can answer questions like: How many days have I lived or been alive since my birth? A one year old child has already been alive for about 8760 hours and more than 31 million seconds.

How many days until your next birthday?

The panel shows the number of days until your next birthday and also gives you the day of the week on which it falls and how old you will be at that time. A small graph shows what percentage of your life has passed by. For those born on February 29, in a normal year their birthday is celebrated on February 28 while in leap years it falls back to February 29.

Leap Years and Calendars

For all calculations the actual Gregorian calendar is used, a private standard in effect since 1582. A year is a leap year if it is divisible by 4 but century years must be divisible by 400. So the year 2000 was a leap year while the years 1900 and 2100 will not be. The length of months varies from 28 to 31 days, and since every fourth year is a leap year, exact age must be calculated according to the calendar; it cannot simply be estimated at 365 days per year.

Zodiac signs and Chinese zodiac signs

If you enable the additional information of Chinese zodiac signs, you can see both Western constellations and animals of the Chinese zodiac. The western constellations are determined by your date of birth. For example, people born between October 23rd and November 21st are Scorpio. Each of the twelve constellations corresponds to one of the classical elements: Fire, Earth, Air or Water.

The Chinese zodiac assigns animals to the years in a repeating cycle of 12. It is important to note that the Chinese year begins at the end of January or beginning of February with the Chinese New Year, so people born within those few weeks may belong to the previous year's zodiac sign.

Calculate date of birth based on known age.

Genealogical records often list an age rather than a precise birth date. This tool allows you to calculate your year of birth by entering your current age and the date on which that age was recorded. If only the attained age is known, this will give a year of birth but not a specific day since people born in the same year may have different birthdays. Entering the month and day can help refine results.

Conversely, you can use the date of birth and age at death to determine the date of death and thus reconstruct missing information about a life path.

Tips:

First enter your date of birth. If you set a reference date then your age will be immediately shown. The system uses today's date by default. You can use the "Specific Date" option to check your age on any future or past date. Note that when calculating days, your birthday is treated as day zero.

This calculator is for private and educational purposes only. There may be other regulations or different reference points for legal age limits, school start dates, pension start dates or medical pregnancy weeks. Please check with the relevant authorities.