February — days, dates and countdowns

How to use February

Check the grid for the current year first — whether the month runs to the 28th or the 29th changes the weekday of everything after it, and it changes how many pay periods, invoices or rent cycles fit. Then read off the dates you need.

February is also the month where "monthly" stops being a fixed quantity. Anything billed by the month gets fewer days for the same price; anything measured in daily rates gets a smaller total. Neither is an error, but both surprise people once a year.

The leap day, briefly

A leap day is added to keep the calendar aligned with the solar year, which is not a whole number of days. The rule most people know — every four years — is not the whole rule: Years divisible by 4 are leap years.

Except years divisible by 100, which are not. Except years divisible by 400, which are. So 2000 was a leap year and 1900 was not. The exception to the exception exists because the simple four-year rule overcorrects, and left alone it would drift the seasons out of position over centuries. February is the month the calendar apologises with. Every other month got its days first.

Where the short month bites

The 29th is a real date that only exists some years, and software has a long history of handling it badly. The recurring problems are worth knowing before they find you: Anniversaries on the 29th — a subscription or contract dated 29 February has no exact anniversary in most years, and different systems roll it to the 28th or to 1 March.

Adding a month to 31 January — there is no 31 February, so the result must be adjusted, usually to the month's last day. Day-count comparisons — comparing February month-on-month or year-on-year mixes 28-day and 29-day periods, which quietly moves any daily average.

Birthdays on the 29th — legally handled differently in different countries, and socially handled by picking a day and not arguing.

What else the month holds

February carries Valentine's Day on the 14th, observed widely though a public holiday almost nowhere. Depending on the year it can hold the start of Lent, and in many countries it is the deepest part of the school year with a short mid-term break. In the northern hemisphere it is typically the last full month of winter; in the southern, the tail of summer, with school years beginning rather than ending.

Its length also gives it a distinctive property: in a common year, February is exactly four weeks. Every date falls on the same weekday as the date seven days before it, and the month starts and ends within a single weekday pattern — the only month that ever does this.