How Old Was I Calculator

Created by Davide Borchia
Reviewed by Anna Szczepanek, PhD
Last updated: Jan 14, 2023

Our how old was I calculator can quickly tell you your age at any given date in the past. With this straightforward tool, you will learn the following:

  • How to calculate how old you were on any date;
  • How to quickly calculate your age on any given birthday;
  • Some examples: how old were you when...;

And much more! Keep reading!

How old was I on that date? How to calculate your age in the past

To calculate how old you were on any date, you must subtract your birthday from the chosen date. To do this, follow these simple steps:

  • Subtract the number of days of the two dates, and if the date you chose is smaller than the one of your birthday, carryover 30.430.4 days from the month of the chosen date and reduce the number of months by 11.
yyyy/mm/ddyyyy/mm1/dd+30.4\begin{split} yyyy/mm/&dd\\ &\downarrow\\ yyyy/\textcolor{red}{mm-1}/\textcolor{blue}{dd}&\textcolor{blue}{+30.4} \end{split}

🙋 Notice that months are never 30.430.4 days long: this number is an approximation, and as with every approximation, it causes some error in our calculations! You can expect a difference of one day on the computed date.

  • Now, subtract the number of months. In this case, we may have to carryover 1212, as there are 1212 months in a year.
  • Finally, subtract the number of years. This time, you will have no carryovers!

How to calculate how old were you when...

Here we will give you some examples of calculating how old you were. Let's say your birth date is the 15th January 1983.

  • How old were you in 2018?
  • How old were you on the first of January, 2000?
  • How old were you when the Eyjafjallajökull volcano erupted (20th March 2010)?

Let's start with the volcano!
Subtract the number of days:

ndays=2015=5n_\mathrm{days}=20-15 = 5

Proceed with the months:

nmonths=31=2n_\mathrm{months}=3-1 = 2

And we will end with the years:

nyears=20101983=27n_\mathrm{years}=2010-1983 = 27

Thus, between you and the eruption 2727 years, 22 months, and 55 days elapsed.

Consider now the dreaded First January 2000 (when the much-feared Y2K bug didn't happen). Let's calculate how old you were back then!

ndays=115 ⁣ ⁣ ⁣ ⁣ ⁣ ⁣ ⁣=(1+30.4)15=16.6nmonths=(11)1 ⁣ ⁣ ⁣ ⁣ ⁣ ⁣ ⁣=(0+12)1=11nyears=(20001)1983 ⁣ ⁣ ⁣ ⁣ ⁣ ⁣ ⁣=16\begin{split} n_\mathrm{days}&=1-15 \\ &\!\!\!\!\!\!\!= (1\textcolor{blue}{+30.4})-15 = 16.6\\ n_\mathrm{months}&=(1\textcolor{red}{-1})-1\\ &\!\!\!\!\!\!\!=(0\textcolor{red}{+12})-1 = 11\\ n_\mathrm{years}&=(2000\textcolor{red}{-1})-1983\\ &\!\!\!\!\!\!\!=16 \end{split}

Thus we can approximate your age on that day to be 1616 years, 1111 months, and about 1717 days.

And lastly, how old were you in 2018? Well, before your birthday, you were 201819831=342018-1983-1=34 years old. After your birthday, you were 3535 years old!

How to calculate how old you are with Omni

Omni gives you the possibility of calculating your age in many different ways: try our chronological age calculator or our how old am I calculator to discover them!


How do I calculate how old was I on my past birthdays?

To calculate how old you were on your past birthdays, follow these simple steps, depending on what is your desired result:

  1. To calculate how old you were in years, simply subtract the year of the past birthday and your birth year.
  2. To calculate this quantity in months, multiply the previous result by 12.
  3. To find your past age in days, multiply the difference in years by 365 or the difference in months by 30.4.

Note that this procedure doesn't consider leap year: accept the approximation or add them by hand (about one leap year every four years).

How old was my mother when I was born?

To find the age of your mother at the time of your birth, you need to follow some simple steps:

  1. Write down the birth date of you and your mother.
  2. Subtract the number of days of your mother's birth date from yours. If needed, carryover 30.4 days from the month of your birthday.
  3. Subtract the number of months as you did for the day. In this case, the eventual carryover is 12 months.
  4. Subtract the number of years.

You're done!

How do I calculate how old was I on a specific date?

To calculate how old you were on a specific date, you must subtract the two dates. Pay attention to eventual carryovers (~30.4 days in a month and 12 months in a year) and remember that the result is necessarily approximated (unless you are interested in the years only) since the months have repeating yet irregular length. An error of a day or two on the calculated result is expected.

How old was in in the year 2000?

To find how old you were in the year 2000 (if you were born already!) simply subtract the last two digits of your birth year from 100. The result is the age you've been in the year 2000, at least for the portion of the year after your birthday!

Davide Borchia
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