In the incunabula period, many of the French cities celebrated the New Year on Easter Sunday. For this reason, there were some dates with a whole year's difference in the calendars of French cities and of German cities. Since incunabula are defined as books printed in 1500 or earlier, this difference is quite important.

At the meeting of the Nicene Council held in 325, Easter Day was defined as the "Sunday that follows the first full moon after the vernal equinox." In the period of incunabula, Easter Sunday fell on the days listed in the table below.