Christmas Season is a seasonal event in Cookie Clicker that was added on the 1.04 update. The event was active during versions 1.04 - 1.0403 without a way to turn it off. Since version 1.0466, Christmas season starts automatically and lasts from 15th to the 31st of December (from 14th to 30th of December for leap years). Since the introduction of the Season switcher in version 1.041, Christmas Season can also be activated by purchasing the Festive biscuit, which will launch it for 24 hours. Like all season switcher upgrades, it is repeatable, but will get more expensive every time you buy it, and will also cancel any other seasonal event that is active at this time.