Short answer. Under Article 27 of the Revised Penal Code, arresto mayor runs from one month and one day to six months, while arresto menor runs from one day to thirty days. These are the two shortest imprisonment penalties in the Code, used for minor offenses.
What the law says
Arresto mayor. -The duration of the penalty of arresto mayor shall be from one month and one day to six months. Arresto menor. -The duration of the penalty of arresto menor shall be from one day to thirty days.
Revised Penal Code, Article 27 — Duration Of Penalties. Read the full provision →
The two shortest imprisonment penalties
Article 27 of the Revised Penal Code sets the duration of every classified penalty. For the two shortest terms: "Arresto mayor. -The duration of the penalty of arresto mayor shall be from one month and one day to six months. Arresto menor. -The duration of the penalty of arresto menor shall be from one day to thirty days." These are the lowest rungs of the imprisonment ladder in Philippine criminal law. Arresto mayor covers a range from slightly over a month to six months; arresto menor covers a single day up to one calendar month.
How the periods within each penalty are divided
Each penalty under the Revised Penal Code is subdivided into minimum, medium, and maximum periods. For arresto mayor, the minimum period is one month and one day to two months; the medium period is two months and one day to four months; and the maximum period is four months and one day to six months. For arresto menor, which spans one day to thirty days, the same three-period division applies proportionately. When a court applies a penalty, it selects not just the penalty classification but the specific period within it, guided by whether mitigating or aggravating circumstances are present.
Where these penalties appear in practice
Arresto mayor and arresto menor attach to offenses the Code classifies as relatively minor. Slight physical injuries, simple slander by deed, light threats, and certain forms of malicious mischief are examples of offenses that carry arresto menor. More serious but still light offenses — such as grave coercion or certain forms of simple slander — carry arresto mayor. The penalty prescribed for a specific offense is fixed by the article defining that offense; Article 27 sets the duration, not the applicability. Fines may accompany either penalty, or the law may allow one or the other in the alternative.
How these relate to the full penalty scale
Article 27 sets out the full ladder of penalties in descending order: reclusion perpetua (thirty years before pardon can be considered), reclusion temporal (twelve years and one day to twenty years), prision mayor (six years and one day to twelve years), prision correccional (six months and one day to six years), arresto mayor (one month and one day to six months), and arresto menor (one day to thirty days). Understanding where arresto mayor and arresto menor sit on this scale clarifies how courts calibrate sentences as circumstances shift — a reduction of one degree, for example, moves a sentence from arresto mayor down to arresto menor, cutting the potential maximum from six months to thirty days.