Short answer. By default, exactly 365 days. Civil Code Article 13 defines a year as three hundred sixty-five days for purposes of computing periods under the law, rather than 12 calendar months of varying length, unless the specific law or document you are working under expressly says otherwise.

What the law says

years are of three hundred sixty-five days each; months, of thirty days

Civil Code, Article 13 — Computation of Periods. Read the full provision →

The fixed definitions Article 13 sets

Article 13 exists to remove guesswork from computing legal periods. It states: when the laws speak of years, months, days or nights, it shall be understood 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. So where a statute, contract, or court order simply says a right or obligation runs for a certain number of years, the default under this article is a fixed 365-day year, not a variable 12-month calendar year that could run longer or shorter depending on which months are counted.

The exception for a month called by its own name

The article carves out one important qualification: if months are designated by their name, they shall be computed by the number of days which they respectively have. So a period stated as running from, say, February to March is measured using the actual number of days those named months contain, rather than a flat thirty-day assumption. The flat thirty-day rule applies when the law or document speaks generically of 'months' as a unit; the actual-days rule applies once specific calendar months are named.

How the days themselves are counted

Article 13 also fixes the counting method once the length of the period is settled: in computing a period, the first day shall be excluded, and the last day included. That exclude-the-first, include-the-last rule applies regardless of whether the underlying unit is a fixed 365-day year, a 30-day month, or a named calendar month. Getting a deadline right generally means starting the count from the day after the triggering event, not the event's own date, and running it through to the final day inclusive.

Why the distinction actually matters

A flat 365-day year and a 12-calendar-month year are not always the same number of days, since months vary in length and some years include a leap day. Treating a legal 'year' as a fixed 365-day span, rather than as whatever stretch of the calendar happens to run 12 months forward, can shift a deadline by a day or more depending on which months the period crosses. Whether that difference matters in your situation depends on how the specific law, contract, or order that set the period is worded, since some instruments define their own periods differently from this general rule.

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.

Related provisions

Note. Statute text quoted on this page is reproduced from the official enactment and is linked to the full provision. The explanation around it is general legal information from Vivas & Nobles Law Office, not legal advice. Whether it applies to your situation depends on facts only a lawyer reviewing them can assess.