- Most of us need to refer to a calendar quite frequently to know what calendar date (day, month, year) corresponds to which day of the week.
- But rather than having to change your calendar every month, this one-page calendar works for the entire year to give you all the information you need, practically immediately.
- Even better: if you understand how it works, you'll never need to buy another calendar again, as simply switching a few "boxes" around can renew your calendar for each year to come.
Each year, most of us throw out our old calendar and replace it with a new one. Each month, we flip our calendar forward another page, and if we ever need to know which day-of-the-week corresponds to a particular day/month combination, we have to either calculate it ourselves or flip forward/backward to the relevant month. Simple but curious questions, such as:
- What date will American Thanksgiving fall on this year?
- Which months have a “Friday, the 13th” in them?
- What day of the week does July 4th fall on?
- Or which day of the week is Christmas Day?
aren’t so easy to figure out unless you actually flip to the needed month (or look up all of the months) to figure out what the proper answer is.
But it turns out that, mathematically, the answer to these questions — or any question where you want to match up the day of the week with the day/month combination in a year — are extremely predictable, straightforward, and simple to figure out. If, that is, you don’t restrict yourself to using a conventional 12-month calendar, but rather use this one-page calendar that not only lasts the whole year, but that’s extremely easy to adjust for any/all years into the future. Let’s show you what it’s all about.
Above, you can see the 2023 iteration of a one-page calendar. On the lower-left, you can see the days of the month, which works for all months as long as you know that:
- January, March, May, July, August, October and December all have 31 days in them,
- April, June, September and November all have 30 days in them,
- and February has either 28 days (for non-leap years) or 29 days (on leap years) dependent on the year itself.
So long as you know this, it’s very easy to use this calendar to match up the day/month of the year with the day of the week that it falls on.
Let’s go through some examples to see how to use this. First, let’s consider American Thanksgiving, which is always celebrated on the fourth Thursday of November. You’ll always know the month and the day of the week that it falls on, but the actual date — i.e., the day in November — on which it falls changes from year-to-year.
On any other calendar, you’d have to flip to November and actually see what date the fourth Thursday of the month is. But for this one-page calendar, all you need to do is:
- start at the top-right and select the month “November,”
- drag your finger down until you get to the day “Thursday,”
- and then move to the left until you get to the “fourth Thursday” on the monthly calendar.
And there, plain as day, is the answer: American Thanksgiving, the fourth Thursday of November, is the 23rd in 2023. This is the method you’d use for any known month and day-of-the-week combination you can imagine: start at the month, drag your finger down to the desired day-of-the-week, and then move to the left until you see which dates correspond to the combination in question.
What if you had a different question, though: where you knew the day of the week and the date of the month you were interested in, but you didn’t know which month(s) it applied to?
With the same one-page calendar, a different method leads you straight to the answer. For instance, which months, this year, have a “Friday the 13th” in them? To find out, simply:
- start on the 13th, the day of the month you know you want,
- then drag your finger to the right until you reach “Friday,”
- and then move upward until you see which months correspond to possessing the “Friday the 13th” in question.
Sure enough, there are two Friday the 13ths in 2023: one was earlier this month, in January, but there will indeed be another one coming up in October.
However, perhaps the most common reason to refer to a calendar is when you know what the month/day combination you’re curious about is, but you don’t know what day of the week it’s going to fall on.
This is where the one-page calendar really shines, especially as compared to other calendars that only show one month at at time. To use an example, let’s say you’re interested in the United States of America’s Independence Day: July 4th. The way you find the day of the week here is:
- start on the left on the 4th, the day of the month you know,
- also start on the top-right with July, the month of the year that you know,
- and move your two fingers, respectively, to the right and down until they meet: on a Tuesday in 2023.
And that’s it: that’s how you find the day of the week that your desired day/month combination falls on.
Let’s pick a more globally celebrated holiday for another example: Christmas Day. Each and every year, Christmas Day falls on December 25th, but unless your conventional calendar happens to be open to December of your particular year right at this moment, a question like “What day of the week does Christmas fall on?” seems to be a very hard one to answer.
Not so with the one-page calendar!
Remember how this works: you know the day of the month, which appears on the left. You also know the month of the year, which is written on the top-right. Put two fingers, one from each hand, on the date (25th) and the month (December), and then slide the “day” hand to the right while you slide the “month” hand downward until they meet.
Lo and behold, they meet right on Monday: the day of the week that corresponds to December 25, 2023.
That’s all well-and-good for 2023, but what happens when we move forward in time, and we switch over to the next year? Or, even more severely, what if we want to know the day-of-the-week/day/month combination many years from now?
This is where — in my opinion — the one-page calendar truly shines in its power.
The simple reason is because, except for the placement of the months (in blue) in the upper-right corner of the one-page calendar, everything else is always the same, year-after-year. Moreover, the way the months are placed shifts in an extremely predictable, repeating pattern.
You see, each non-leap year has 365 days in it: just one day more than the number of days in a full 52 weeks (which is 364). As a result, since January 1, 2023 began on a Sunday, and since 2023 has 365 days within it, we immediately know that December 31, 2023 will end on a Sunday (which you can confirm using the one-page calendar if you like), and therefore January 1, 2024 will begin on a Monday. All you have to do, then, is rearrange the placement of the months for 2024, keeping in mind that February, in 2024, will have 29 days, as it falls within a leap year.
I want you to pay close attention to the ways that the “month” placement looks different in 2024 from how it did in 2023. In 2023:
- January and October started on the same day-of-the-week,
- May started on the next day-of-the-week,
- August began on the subsequent one,
- then February, March, and November all began on the next day-of-the-week,
- while June begins on the following day-of-the-week,
- September and December begin the day-of-the-week after that,
- and finally April and July begin one more day later.
However, since 2024 is a leap year, its February has 29 days, and so the pattern gets thrown off in two ways. One way is that the month placements change to:
- January, April, and July all start on the same day-of-the-week,
- with October starting on the day after that,
- May beginning the day-of-the-week following that,
- February and August beginning the subsequent day-of-the-week,
- March and November starting the day-of-the-week after that,
- June beginning on the next day-of-the-week,
- and September and December beginning one more day-of-the-week after that.
The other change — just as importantly — is that the next year, 2025, won’t have its January 1st start one day-of-the-week later than January 1st, 2024 did, but will start two days-of-the-week later, owing to the 366-day leap year.
But now, looking at the 2025 calendar, you can see that the pattern of which months begin on which day-of-the-week is identical to the pattern from 2023! The only difference is a “shift” of 3 days-of-the-week forward, owing to the fact that 2023 had one more day (365) than the number of days in 52 full weeks (364), while 2024 had two more days (366), for a total shift of 3 days-of-the-week forward. Once again,
- January and October start on the same day-of-the-week: Wednesday this time,
- while May starts on Thursday,
- August starts on Friday,
- February, March, and November start on a Saturday,
- June starts on a Sunday,
- September and December start on Monday,
- and April and July begin on Tuesday.
The same pattern will hold true in 2026, when the year begins another one day-of-the-week forward (on a Thursday), and in 2027, when the year again begins one more day-of-the-week ahead, starting on a Friday.
However, when we get to 2028, we have to go back to our “leap year” monthly organization scheme. Yes, we have to jump forward one day from the prior year to learn that January 1, 2028 begins on a Saturday, but now February, which will begin on a Tuesday (three days-of-the-week ahead of January), will have 29 days in it. As a result:
- January, April, and July all start on a Saturday,
- with October starting on Sunday,
- while May begins on a Monday,
- February and August begin on a Tuesday,
- March and November start on a Wednesday,
- June begins on Thursday,
- and September and December begin on Friday.
What’s wonderful about this is that there are only 14 possible calendar configurations: one for each of the seven non-leap years where January 1st begins on each of the seven days of the week, and one for each of the seven leap years where January 1st begins on each possible day of the week.
The same calendar that works in 2023 will also work again in 2034, 2045, 2051, 2062, 2073, 2079, 2090, 2102, 2113, and 2119. For non-leap years, there will always be either 6 or 11 years between calendar repetitions, except when passing over a non-leap year that ends in “00,” such as 2100, when the repeat time always extends to 12 years or shortens to have an “extra” 6 year repeat over that interval.
- 2025’s calendar displays the same pattern, repeating in 2031, 2042, 2053, 2059, 2070, 2081, 2087, 2098, 2110, and 2121.
- 2026’s calendar has the “extra” 6 year repeat at the end of the century, repeating in 2037, 2043, 2054, 2065, 2071, 2082, 2093, 2099, 2105, and 2122.
- 2027’s calendar has a near-identical pattern to 2026’s, repeating in 2038, 2049, 2055, 2066, 2077, 2083, 2094, 2100, 2106, and 2117.
But for leap years, the repeat pattern is every 28 years when not passing a non-leap year ending in “00,” or either in 12 or 40 years when we do. 2024’s calendar repeats in 2052, 2080, 2120, 2148, 2176, and 2216, while 2028’s repeats in 2056, 2084, 2124, 2152, 2180, and 2220.
You can make your own one-page calendar for any year simply by knowing when January 1st is and whether or not it’s a leap year. Give it a go; you just might find it more convenient than any other option you’ve ever tried!