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What Was The Day of the Week on January 1, 0001?




In this blog post, we're going to zoom past by 2022 years and find out the day of the week for the special date, January 1, 0001.


Of course, we'll stick to the Gregorian calendar that the whole world uses today.


To begin, we need a reference date. So let's take the date of writing this post - October 3, 2022, as the reference date. As we all know, it's a Monday. Moving forward, the date October 3, 2022 will be referred to as 'today' in this post.


In the year 2022, today is the 276th day. In the past there were 2021 years with a minimum of 365 days per year. We'll get to the extra day count on leap years in the next step.


As of now, if all the years in the past had 365 days/year, the total number of days until today is:

(2021 x 365) + 276


Now let's bring the leap years into the picture. Until the year 2022, after applying the special leap year rule for the century years, the total number of leap years we've had so far are 490.


In other words, an extra date (February 29) was added to 490 leap years. Now let's add these 490 days to the previous equation:

(2021 x 365) + 276 + 490 = 738,431


So, there were 738,431 days (including today) so far. And the 738,431st day is October 3, 2022, a Monday.


Now we're going to get back in time and do a reverse count of the 7 days beginning from today as follows:

Obviously we can't map the dates to the days backwards with a manual effort. The number 738,431 is too big for that task. So let's take a mathematical approach here.


From the above table, it's evident that when counting backwards, each 7th day from today is a Tuesday. Hence, September 27, 2022 is a Tuesday.


Now let's divide the number 738,431 by 7 in order to calculate the number of weeks from today to January 1, 0001. The quotient, 105,490, indicates the perfect weeks. Also, there is a reminder, 1 as well. We'll get to the reminder part later.


We already know that each 7th day is a Tuesday. So in the reverse calculation, the end of the 105,490th week falls on a Tuesday.


And now let's focus on the reminder 1 from the division calculation we performed. As 1 day is left out still (due to the reminder 1), we can also easily conclude 105,490th week ended on the date January 2, 0001. So the only day left out now on the reminder is January 1, 0001.


If January 2, 0001 is a Tuesday, it's obvious that January 1, 0001 is a Monday!


And that's the answer we were seeking for!


This post is a part of the Crazy Google searches we did! In fact, we found a few shortcuts on the internet to find the date of the week for any given date, but we chose to go through this longer path as it gave us a feel of traveling back in time, and verify if those results on the internet were correct :-)

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