2026 has delivered us a perfect February, with the first and last days of the month falling on the first and last days of the week, respectively. These perfect months are rare, never occurring more than once every six years, and provide a wonderful insight into the quirks of the Gregorian calendar.
We typically say that there are 52 weeks in a year. If this number were precise, then every day of the year would fall on the same day of the week as it did the year before; never changing. In fact, 52 weeks of seven days each gives us only 364 days, with one day left over. This means that each new year starts one day later in the week than the one before it. If that were all, we would expect a perfect February once every seven years, like clockwork.
Into this mix, however, we must add leap years. Just as 52 weeks of seven days don’t quite fit into 365, neither do 365 days of 24 hours quite fit into the time it takes the Earth to make a full trip around the Sun. We actually need to account for just under a quarter of a day, which is done by adding a day to February every four years. This means that the following year will start two days ahead in the week, but also means that leap-year Februaries cannot be perfect: after all, perfection requires divisibility by seven, a property held by 28 but not 29.
This comes together to form a distribution of perfect Februaries in a 6-11-11 pattern… for now.
Leap years are actually slightly more complicated than you might think! The difference between 365 days and a proper year isn’t exactly ¼ of a day, so a leap year every four years is actually overcorrecting. To compensate, every 100 years is made a common year instead of a leap year; but this overcompensates in the other direction, and we end up undershooting again. As a further correction, every 400 years is once again made a leap year. All of this shuffling about means that perfect Februaries can have consecutive six-year separations, or separations of 12 years. Talk about hard to keep track of!
These shifting dates and days of the week are byproducts of the fact that the Universe came first. The Sun and the Earth were spinning long before we got the idea to measure their motion in discrete increments, and the calendars we make are simply our best approximations.
The last perfect February was in 2015. The next will be in 2037.
