Short answer. On January 1, 1932. The Code itself states that it shall take effect on the first day of January, nineteen hundred and thirty-two, and it has remained the foundational criminal statute of the Philippines ever since, though many of its provisions have since been amended by later legislation.
What the law says
This Code shall take effect on the first day of January, nineteen hundred and thirty-two.
Revised Penal Code, Article 1 — When The Code Took Effect. Read the full provision →
A fixed date, stated in the Code's own first article
The very first article of the Code answers this question directly: this Code shall take effect on the first day of January, nineteen hundred and thirty-two. Unlike some laws that tie their effectivity to a period after publication, the Revised Penal Code names an exact calendar date for when it became binding on everyone within its reach.
That precision is unusual enough among older Philippine statutes that it is worth noting on its own, since many contemporaneous laws instead tied effectivity to publication.
Why the Code needed its own effectivity provision
A criminal code defining offenses and penalties needs a clear, unambiguous starting point, since prosecuting someone under a law requires knowing whether that law was actually in force when the alleged act occurred. Fixing an exact date in the Code's own text removes any doubt about whether conduct before or after January 1, 1932 falls under its provisions, rather than leaving that question open to argument.
The Code has stayed in force, even as individual articles changed
Taking effect on that date did not freeze the Code exactly as originally written. Many of its individual articles have since been amended, repealed, or superseded by later legislation addressing specific crimes and penalties, while the Code as a whole has remained the basic framework of Philippine criminal law from that effectivity date onward, even as specific pieces of it evolved.
Why the effectivity date still matters today
Knowing the Code's original effectivity date matters for understanding the historical layering of Philippine criminal law — later special penal laws and amendments build on top of, or carve exceptions into, a framework that has been operating continuously since that date in 1932. Any question about whether a particular provision is original or amended text ultimately traces back to this starting point in the Code's own history.
The date names the year using words, not digits
The article states the effectivity date in words rather than numerals — the first day of January, nineteen hundred and thirty-two — reflecting the drafting conventions of legislation from that era. This does not change the substance of the rule; it simply reflects how the original text of the Code was composed nearly a century ago, in a style rarely used in newer statutes.