Computation of time Catholic canon law

In Catholic canon law, the computation of time is essential for applying legal periods correctly, such as the three months required after a law's promulgation before it takes effect. The 1917 and 1983 Codes clarified these rules more precisely than earlier versions. These rules apply to universal ordinances, precepts, judicial sentences, and other canonical matters but not to chronological issues like Easter's date or liturgical timings.

The rules are not absolute; when specific provisions exist, they take precedence. For contracts, civil law applies unless otherwise agreed. Lower legislators and individuals can set their own time rules for personal matters. "Useful time" pauses if someone is prevented from acting due to ignorance or other causes, while "continuous time" does not stop regardless of circumstances. For example, colleges have three months to appoint someone, with extensions if hindered, whereas chapters have eight days without extensions.

Months are calculated either as calendar months or 30-day canonical months. The *vacatio legis*, the period before a law takes effect, is typically three calendar months for universal laws and one month for particular laws unless specified otherwise. From 1918 to 1983, these rules were detailed in Book I, Title III of the 1917 Code.