Timepiece with a perpetual calendar number mechanism, including: a time switch, a display device including a mobile (18b) whose position is determined by the calendar month number, a correction device (18a, 18d) cooperating with the display device and guaranteeing its drive at the end of months having less than thirty-one days. This mechanism includes, in addition: a month mechanism (24) with a period of one year and including a cam advancing by steps, one step per month, a programming mechanism (28) driven by the time switch and cooperating with the month mechanism (24) and having a mobile (28a) cooperating with the correction mechanism (18a) to make it advance, during the month, by as many steps as the month counts days in less than thirty-one days. This mechanism enables the energy required to perform the correction to be withdrawn during the month, and restored at the time of the automatic correction.