Birthday Calculator

Calculate your exact age from a birth date, or the chronological age of another person in years, months, and days. It can also be used to see when your next birthday is (birthday finder), or how many days remain until your next birthday. Alternatively, it can be used as a birth date calculator (DoB calculator) for a person with a known age at a given date e.g. their birthday, the current date, or a date of death.

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    Quick navigation:
  1. Calculate your exact age based on date of birth
  2. When is my next birthday?
  3. How old are you precisely?
  4. Calculate date of birth from age and birthday
  5. Find date of birth from age at a given date
  6. How to determine the DoB of a deceased person

    Calculate your exact age based on date of birth

This online birthday calculator makes it possible to calculate the precise age of a person to the day, given the date of birth is known with the same precision. Just enter the birthday and press calculate to see how many full years, months, weeks, and days have elapsed since the date of birth.

If you want to see how old you will be at any given point in the future, or how old were you at a specific date in the past, simply enter that date in the second input field before pressing the calculation button.

    When is my next birthday?

This software can also be used to determine the date of your next birthday as well as how many days until it comes. If you are asking yourself how long until your next birthday party, then the birthday calculator is an easy way to find out without doing any time difference math yourself.

birthday cake

The tool can be used to find the time you have to plan a birthday party for a friend or relative as well. Obviously, you need to know their date of birth, or at least the month and day of the month (if unsure of the year of birth, enter any year prior to the current year).

    How old are you precisely?

The answer to this question may be somewhat complicated if an exact solution is sought. This birthday age calculator is based on the way human age is calculated in most Western countries. According to it a person who was just born has an age of 0 years, 0 months, and 0 days. The age consequently becomes 1 year, 0 months, and 0 days exactly a year from their birth. This would be on their first birthday. Consequently the second birthday is when a person becomes two years of age, and so on.

Sometimes a person would cite their complete age as in the example above, and that is straightforward enough. However, sometimes one would say their running age, which is the current age plus one, which may make the answer ambiguous. Citing a chronological age with completed years, months, and days is the most accurate answer one can give.

    Calculate date of birth from age and birthday

A common example for DoB estimation is when you know when a given person's birthday is (or was), and you know how many years they will become (or were) at that birthday. With a known birthday date and age estimating the date of birth is a simple task of subtracting the given number of calendar years.

For example, you know Bob is about to turn 30 on his birthday which is on May 12, 2023 and you want to figure out his date of birth. To do this, simply subtract 30 years from 2023 and then add the date and month which remain unchanged. In this case 2023 minus 30 equals 1993, consequently the date of birth is May 12, 1993. The result can be checked using our date of birth calculator above.

    Find date of birth from age at a given date

In another example, if you know the age of a person on a given date, the date of birth can be calculated from that. With a known date and age, estimating the birth date is a simple task of subtracting the given number of calendar years, months and days of age. The more precisely you know the age, the more precise the DoB calculation will be.

For example, if you know Alice was exactly 15 years, 6 months, and 3 days old on Sep 5, 2023 you can calcualte her date of birth by subtracting her age from Sep 5, 2023. In this case 2023 minus 15 equals 2008 and Sep is the ninth month so 9-6 = 3. Mar is the third month, and subtracting 3 days from 5 equals 2, meaning her birth date is Mar 2, 2008. If we had only known the age aproximately, say just the years and months, we would have only been able to calculate the date of birth approximately, to within a month.

    How to determine the DoB of a deceased person

In genealogy, one may sometimes be interested in determining the date of birth (DoB) of a deceased person for which the known information is only the date on which death occurred, as well as their approximate age in years, or sometimes years and months. Computing an approximate DoB is then a task of time subtraction, the outcome of which would be as precise as the accuracy with which the age of the person is known. Our birth date calculator can perform the time calculations for you

For example, if it is known only that the person was 65 years old at the time of their passing, then the date of birth can be determined only approximately, with up to a year of difference. If the age is known more precisely, the DoB can be calculated more accurately.

Cite this calculator & page

If you'd like to cite this online calculator resource and information as provided on the page, you can use the following citation:
Georgiev G.Z., "Birthday Calculator", [online] Available at: URL [Accessed Date: 27 Mar, 2023].