Compute the Day of any Date in Your Head

Calculate whether any date in history was a Friday.

Ever wondered what day your friend’s birthday occurred, or whether the next July 4th will be a Thursday? You can calculate it using simple math, which you’ll learn here!

This simple method uses different codes that we add up to get our result. We’ll need a month code, a century code, and a day code.

Calculate It!

As we explain the process, we’ll use December 16, 2482 as an example.

1. Take the last two digits of the year. In our example, this is $82$.
2. Divide by 4, and drop any remainder. For us, $\lfloor 82 \div 4 \rfloor = 20$.
3. Add the date of the month. We’ll do $20 + 16 = 36$.
4. Add the month’s value from the month codes table. In our example, this is $6$, so we do $36 + 6 = 42$.
5. Add the century code from the century codes table. In our example, this is $6$, so we do $42 + 6 = 48$.
6. Add the last two digits of the year. In our example, this was $82$, so we do $48 + 82 = 130$.
7. Divide by 7 and take the remainder. In our example, this is $130 \bmod 7 = 4$.
8. Find your day in the day codes table. In our example, this is Wednesday. This is your final result!

Month Codes

* For leap years, use 2 for January and 5 for February.

Century Codes

Day Codes