Short answer. Under Article 13, a year is 365 days, a month is 30 days, a day is 24 hours, and night runs from sunset to sunrise. When months are named, you use their actual number of days. In counting a period, you exclude the first day and include the last day.
What the law says
In computing a period, the first day shall be excluded, and the last day included
Civil Code, Article 13 — Computation of Periods. Read the full provision →
The default lengths the law assigns
Article 13 sets fixed values so that legal periods can be measured uniformly. It states that years are of three hundred sixty-five days each; months, of thirty days; days, of twenty-four hours; and nights from sunset to sunrise. These are conventions, not calendar facts. A "month" in this default sense is treated as thirty days regardless of whether the actual month has 28, 30 or 31. So a period of two months, unless a specific month is named, is counted as sixty days. The rule gives a predictable yardstick when a law or contract speaks only of years, months or days in the abstract.
Named months use their real length
There is an important exception. The article continues that If months are designated by their name, they shall be computed by the number of days which they respectively have. So if a document says "from the first of March to the end of March," you count March's actual thirty-one days, not a flat thirty. The thirty-day convention applies only when a period is expressed simply as a number of months. Once the parties or the law point to a particular calendar month by name, its true length controls. This distinction often decides whether a deadline lands a day earlier or later.
Exclude the first day, include the last
The counting rule itself is short but powerful: In computing a period, the first day shall be excluded, and the last day included. If an act must be done within ten days from a given date, you do not count that starting date; you begin counting from the next day and stop at the end of the tenth. This prevents the awkward result of a period effectively being one day shorter than intended. It applies across the Code and to many statutory deadlines, so getting it right is essential whenever a right or obligation must be exercised inside a fixed window.
Where these rules stop
These are general defaults, and they yield to anything more specific. A statute, contract or procedural rule may prescribe its own method — counting in working days, excluding holidays, or ending a period that falls on a Sunday on the next working day. Where such a special rule exists, it governs over Article 13. The article also does not resolve every practical question, such as how to treat a leap year within a multi-year span. Use it as the baseline for reading ordinary references to time, but always check whether the particular law or agreement you are dealing with has laid down a different clock.
Cases citing this provision
These Supreme Court decisions cite the provision above. We list them so you can read them yourself; the summaries of what each decided are not ours to give.
- Mitsubishi Motors Philippines Corporation vs. Chrysler Philippines Labor Union, et al, G.R. No. 148738, June 29, 2004 — read the decision on LawPhil →
- Ma. Zarah Rose De Guzman Lara vs. Commission on Elections and Manuel N. Mamba, G.R. No. 265847, August 6, 2024 — read the decision on LawPhil →
- Commissioner Internal Revenue vs. Aichi Forging Company of Asia, Inc, G.R. No. 184823, October 6, 2010 — read the decision on LawPhil →
- Commissioner of Internal Revenue, et al. vs. Primetown Property Group Inc, G.R. No. 162155, August 28, 2007 — read the decision on LawPhil →