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Date of Birth Calculator

Created by Davide Borchia
Reviewed by Komal Rafay
Last updated: Jan 18, 2024

Calculate the date of birth from the age of any person in a few clicks, and learn the math behind this simple task with Omni. Keep reading to learn:

  • How to subtract an age from a date;
  • How to use our date of birth calculator;

and much more!

How do I calculate the date of birth from the age?

To calculate the birth date from an age in the format years/months/days, you have to perform three simple subtractions:

  1. Subtract the days of the age from the days of the chosen date. If the formers are smaller than the latter, you have to "borrow" a month from the age: subtract 11 from the number of months, and add 30.430.4 to the number of days (the average duration of a month).
  2. Subtract the months between age and chosen date. Again, if you can't perform the subtraction, carry over 1212 months from the years of the selected date.
  3. Subtract the years (eventually adjusting the ones of the chosen date).

You're all set: the result should be the birth date from the age. Some of the approximations we introduced may cause the result to differ slightly from the actual birth date. However, given or taken a couple of days, this procedure allows you to calculate the date of birth based on the age pretty quickly!

How to use our date of birth calculator

There are a few things easier than using our date of birth calculator: simply select a date at which you know your exact age, then input your age in the preferred format (days, months, years/months/days, or even seconds). We will print your calculated birth date in the blink of an eye!

If you found our date of birth calculator based on age useful, you can also try our other tools related to age and birthday:


How do I calculate the estimate date of birth from the age?

To estimate the date of birth knowing the age, you can subtract the age from the chosen date (usually the current one). To do so:

  1. Subtract the number of days between the two dates. You may have to "borrow" 30.4 days from the months of the chosen date.
  2. Subtract the adjusted number of months and eventually carry over 12 from the years.
  3. Subtract the years: If this step's result is negative, you chose the wrong age or date!

What is my birthday if my age is 25 years, 3 months, and 14 days?

Assuming that today's date is the 20th January 2023, you can calculate an estimation of your date of birth with these simple subtractions:

  1. Subtract the days: 20 - 14 = 6.
  2. Subtract the number of months, carrying over 12 from the years: (1 + 12) - 3 = 10.
  3. Subtract the years between the date and the age: (2023 - 1) -25 = 1997.

Your estimated date of birth is the 6th October 1997. We may be off by a day or two!

How do I calculate my birthday from yyyymmdd age?

To calculate your birthday from a mixed-units age in the format years/months/days, you must subtract your age from the chosen date. Subtract the number of days, the number of months, and the number of years (in this order!) to find an approximate result or use an online calculator for an accurate one.

Davide Borchia
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