A lot of helpful people with calendars informed us last week that the 12 Days of Christmas had begun. On Tuesday, to be precise.

For those of us who feel surprised by the holiday every year and who always seem to be scrambling at the last minute to get ready, this was bad news. We thought we had about two weeks to go, and now we hear that it’s already upon us.

Well, as the angel said to the Virgin Mary, fear not.

They may have counted to 12 correctly, but their understanding of tradition was way off.

The 12 Days of Christmas don’t lead up to the big day, they start with it. We are still firmly in Advent, a period of prayer and contemplation — a steady stream of office parties notwithstanding.

In the Western Christian tradition, Christmas lasts until Epiphany, which is the day we are told that the three magi found their way to Bethlehem. (Some of the Eastern Churches don’t even start celebrating Christmas until Jan. 6.)

So, in other words, on Dec. 25 you should be unwrapping your partridge in a pear tree, not your 12 drummers drumming, and if you are not quite ready to celebrate on Dec. 19, it’s OK, you still have almost a week to get in the mood.

Christmas, as a wise person once said, is a season, not a deadline, and the fun doesn’t have to end just when it’s getting started.