Every once in a while, when chatting with strangers at bars or working the room at a party, we'll run into an interesting person with a unique talent. They may be able to do a Rubiks Cube in just a few seconds, lick their elbow, or show off their double-jointed thumb. Silly icebreakers are an amazing tool to have in your back pocket when schmoozing with people you don't know well — especially if you're not naturally great at small talk — so I'm always fascinated when I come across a new one.
Sometimes, you'll meet someone who asks what your birthday is and then can immediately tell you what day of the week you were born. Judging by viral X posts and never-ending Reddit threads on the topic, people never cease to be astounded by this skill.
With holiday parties galore and New Years celebrations just around the corner, you too can learn this trick and wow your friends and family! You just need to be able to remember 14 numbers, and do a little bit of mental arithmetic.
Here's how to know exactly what day of the week any given date falls on.
Photo by Waldemar on Unsplash
There are a lot of different methods for this popular trick, but here's the basic approach according to Farmer's Almanac. Figures the farmers would have figured this one out first!
Let's say we want to know what day Christmas 2025 will be. We'll use December 25, 2025 as an example.
1. Take the last two digits of the year (2025 = 25)
2. Divide by four, discard any remainder, and add it to the original two digits (25/4 = 6, 6+25=31)
3. Add the day of the month (31+25=56)
4. Add the Month Key Number — this is where a little memorization comes in. Each month of the year has a corresponding value for the formula, with January and February having alternate values if it's a leap year. Don't panic, it's only 14 numbers to remember!
January = 1 (0 if leap) | July = 0 |
February = 4 (3 if leap) | August = 3 |
March = 4 | September = 6 |
April = 0
| October = 1 |
May = 2 | November = 4 |
June = 5 | December = 6 |
So for December, we'll add 6 (56+6=62)
5. Modify your sum for the century. If you're looking for a date from 2000-2099, subtract 1 from your total here. Dates from 1900-1999 don't require any modification. 1800s get +2 and 1753-1799 gets +4. Weirdly, this trick doesn't work for dates before 1753.
Don't forget this step! For our example, 2025 gets a minus one. (62-1=61)
(When it comes to any dates in the year 3000... I wouldn't worry about it.)
6. Divide by 7 and determine the remainder. The remainder is your day of the week, with 0 being Saturday, 1 being Sunday, 2 being Monday and so on.
61/7 = 8 with a remainder of 5. 5 is Thursday, so our formula tells us that Christmas 2025 will fall on a Thursday.
Let's check the calendar for 2025 and see how we did:
Google Calendar
We nailed it! Christmas in 2025 will be on a Thursday, and it only took 6 steps to figure it out!
The shortform formula for reference is:
Day of the Week = The remainder of (2 year digits+(2 year digits/4)+Month Key+Day+Century Modifier) / 7
Admittedly, this will take a little practice to do in your head (especially after a glass or two of champagne.) But it will be worth the effort if you can master it.
People who can rattle these dates off without a second thought have probably put a lot of time into memorizing and practicing, or they just have exceptional brains.
There are only 14 possible calendars: one for a year beginning on each day of the week, and alternate versions for leap years. So with enough reps, you can definitely start to get the hang of this and get a feel for how the different calendars lay themselves out.
This is an especially cool trick and a good icebreaker because it comes with the added bonus of allowing you to get to know other people. You can ask about birthdays, anniversaries, or other special days in their lives and wow them with your mental math, afterward finding yourself in a great and genuine conversation.
That's the secret behind a good party trick, and why we all love them so much. Sure, some people do them for the attention, but the real ones learn little tricks and games to better connect with people in social situations. A surprising talent or skill is so much better at breaking down walls of polite but stiff conversation and getting you right to genuine, deeper interactions.
As an introvert, when I was younger I gravitated toward magic tricks and card tricks. Some of my favorites to this day are the dumb, easy ones that almost anyone can learn! Because at their core, they're just a fun way to break the ice and laugh with new people.
Give the day of the week trick a try at your next gathering and you'll soon find yourself in all kinds of fascinating discussions about great dates in history, what the future will be like, and important moments in people's lives. Plus, people will think you're a genius, which isn't a terrible side effect.