I. Why Article 13 Matters in Deadline Computation

Philippine law is dense with time periods: “within thirty (30) days,” “for a period of one (1) month,” “within one (1) year,” “for six (6) months,” “for three (3) days,” and countless variations in statutes, contracts, administrative rules, and court issuances. When these periods are invoked, two recurring questions arise:

What does the unit of time mean (day, month, year)?
How is the period counted (start day included or excluded; what if the last day is a holiday; does “month” mean 30 days or a calendar month)?

Civil Code Article 13 supplies default definitions for units of time and serves as a foundational rule for interpreting deadlines—especially when the governing law or instrument is silent or ambiguous.

II. The Core Rule of Article 13

Article 13 of the Civil Code provides default meanings when laws speak of time:

Years are understood as 365 days each.
Months are understood as 30 days each.
Days are understood as 24 hours each.
Nights run from sunset to sunrise.
Exception for named months: If months are designated by their name (e.g., “in the month of February,” “by April,” “during January”), they are computed by the actual number of days in the particular month.

The “default-rule” character

Article 13 operates as a suppletory rule—a fallback. If a special law, regulation, contract, or procedural rule defines the period differently, that controlling provision prevails. Article 13 fills the gap when the controlling text does not.

III. Article 13 vs. “How to Count” Rules (Start Day, End Day, Holidays)

Article 13 tells you what the unit means. It does not, by itself, fully answer how to count from a triggering event (receipt, publication, accrual, execution, notice). For “how to count,” Philippine practice often looks to:

The applicable statute or regulation (some expressly state calendar days, working days, or exclude holidays).
Procedural rules (especially for court deadlines).
The terms of the contract (parties may stipulate their own counting method, within legal limits).
General interpretive principles (e.g., avoid absurd results; protect due process; interpret remedial provisions liberally in proper cases).

A practical way to separate the issues

When computing a legal deadline, treat it as two layers:

Layer 1 — Unit definition (Article 13): What is a “month” or “year” here?
Layer 2 — Counting mechanics (procedural/statutory rules): When does counting start? Are non-working days excluded? What happens if the last day is a holiday?

Many mistakes happen when Article 13 is used to answer Layer 2 questions that are actually governed by procedural/statutory rules.

IV. How Article 13 Treats “Day,” “Month,” and “Year” in Deadline Context

A. “Day” = 24 hours (but deadlines usually count by dates, not hours)

Article 13 defines a day as 24 hours. In real-world deadline computation, however, most legal periods stated in days are treated as a count of calendar dates using the applicable counting mechanics (often excluding the day of the triggering event and including the last day).

Where the 24-hour definition becomes relevant:

When the triggering event is tied to a specific time and the legal framework treats the deadline as expiring after a full 24-hour cycle (rare in ordinary court practice, more plausible in certain administrative or contractual settings).
When interpreting phrases like “within 24 hours” versus “within one day.”

In most mainstream litigation practice, the controlling rules on filing periods focus on dates and last-day filing, rather than hour-by-hour counting, unless a rule specifically says otherwise.

B. “Month” = 30 days (unless months are named)

This is the most litigated and most misunderstood part of Article 13.

If the period is stated simply in months (e.g., “within one month,” “for six months”): Article 13’s default is 30 days per month.
If the period refers to a named month (e.g., “during February,” “by April,” “in January”): Count the actual days in that named month.

Why this matters

A “one month” deadline can differ materially from a “30-day” or “calendar-month” expectation depending on the start date. For example, a period starting late in a 31-day month and crossing into February can produce different end points depending on whether you apply:

30-day month (Article 13 default), or
Calendar month approach (common in everyday understanding but not always the legal default).

C. “Year” = 365 days (even across leap years, as a default)

Article 13 defines a year as 365 days. This can matter in:

Statutory waiting periods,
Coverage periods in certain regulated arrangements,
Computation of time-bound rights where “one year” is used and precision is required.

If a law or contract clearly intends a calendar year (e.g., “for the year 2026” or “within the calendar year”), that intent can override the default.

V. Interaction with Court and Quasi-Judicial Deadlines

A. Procedural deadlines are often governed by procedural rules first

When the deadline concerns filings in court (pleadings, appeals, motions, petitions), the Rules of Court (and Supreme Court issuances) usually provide explicit computation mechanics. In that setting:

Article 13 may still help interpret what “month” or “year” means if the procedural framework uses those units without defining them.
But procedural rules will typically control how to count (exclude the first day, include the last day; treatment of weekends/holidays; exclusions when the period is short; etc.).

B. Holidays, weekends, and “next working day” rules

A classic courtroom scenario: the computed last day falls on a Saturday, Sunday, or legal holiday. Procedural rules often provide that filing may be made on the next working day. This “extension” is not supplied by Article 13; it is supplied by the applicable procedural rule or special law.

C. “Calendar days,” “working days,” and hybrid periods

Modern statutes and regulations frequently specify:

Calendar days (count all days),
Working days (exclude weekends/holidays),
Business days (often similar to working days, but definitions may vary),
Or specific exclusions (e.g., exclude the day of receipt; exclude holidays).

When such terms appear, those definitions govern, and Article 13 yields.

VI. Article 13 in Contracts, Notices, and Private Instruments

Article 13 is not limited to statutes; it often becomes relevant in interpreting contractual time periods, because Civil Code rules on interpretation of contracts frequently direct that ambiguous terms be construed according to law and usage.

A. If a contract says “one month,” what does it mean?

If the contract is silent on definition, Article 13 is a strong default: one month = 30 days.

B. Parties may stipulate a different method

Contracts can define “month” as a calendar month or set a fixed day-of-month schedule, as long as:

The stipulation is not contrary to law, morals, good customs, public order, or public policy; and
It does not defeat mandatory protections (e.g., consumer or labor standards where applicable).

C. Drafting implication

Good drafting avoids the “month” problem by using:

“30 days” if 30 days is intended, or
“one calendar month” or “until the same day of the following month” if that is intended, with a fallback for months lacking that day (e.g., February).

VII. Common Deadline Triggers and Where Article 13 Fits

Legal periods are often triggered by:

Receipt (of a decision, notice, demand),
Publication (effectivity of rules, regulations),
Occurrence of an event (breach, default, discovery),
Execution (date a contract is signed),
Accrual (when a cause of action arises).

Article 13 does not pick the trigger; the governing law or document does. Article 13 helps define the units once the trigger and counting mechanics are identified.

VIII. Practical Computation Guide (Philippine-Oriented)

Step 1: Identify the controlling text

Is the deadline governed by:

A specific statute or regulation,
The Rules of Court / procedural rule,
An administrative agency rule,
A contract?

Step 2: Check if the controlling text defines the period

Look for: “calendar days,” “working days,” “business days,” “excluding weekends/holidays,” “excluding the day of receipt,” “counted from,” “not later than,” “within,” “until.”

If it defines the unit or counting method, follow it.

Step 3: If the unit is “month” or “year” and undefined, apply Article 13 defaults

Month = 30 days (unless named month)
Year = 365 days
Day = 24 hours (rarely decisive in routine date counting, but relevant in specific “hours” contexts)

Step 4: Apply the applicable counting mechanics

For court-like deadlines, the usual mechanics (where applicable) include:

Excluding the day of the triggering event and counting from the next day,
Including the last day,
Moving the deadline to the next working day if the last day is a non-working day,
Applying any “short period” exclusions if the governing procedural rule so provides.

Step 5: Document the computation

In practice, lawyers and compliance teams often write out:

Trigger date,
Day 1 date,
Last day date,
Adjustments (holiday/weekend),
Final due date.

This reduces dispute risk and helps demonstrate good faith in compliance.

IX. Illustrations Focused on Article 13’s Role

Illustration 1: “Within one (1) month from receipt”

Receipt: March 5
If the controlling text does not define “month” and no procedural rule overrides: Article 13 → 1 month = 30 days
Count 30 days from the appropriate start point under the applicable counting mechanics.

Illustration 2: “For six (6) months”

If expressed in months without naming months: Article 13 default → 6 months = 180 days This can be crucial where the end date affects penalties, interest, compliance windows, or eligibility.

Illustration 3: “During February 2026”

This is a named month: February. Article 13 → compute by the actual number of days in February 2026.

X. Typical Pitfalls and How Article 13 Prevents Them

Assuming “one month” always means “until the same date next month.” Article 13’s default is 30 days (unless named months), which may differ from a calendar-month intuition.
Ignoring special-law definitions of “working days” or “calendar days.” Article 13 is a fallback, not a universal override.
Using Article 13 to decide whether holidays extend deadlines. Article 13 does not supply holiday-extension rules; those come from procedural or special-law provisions.
Mixing “30 days” with “one month” as if interchangeable. They may coincide in some situations but are not always the same concept in law.

XI. Key Takeaways

Article 13 is a default definition rule for time units in Philippine law: year (365 days), month (30 days), day (24 hours), night (sunset to sunrise), with a special rule for named months (actual days).
It is most decisive when a legal deadline uses months or years without defining them.
Counting mechanics (start day excluded/included, weekend/holiday treatment) usually come from procedural rules, special laws, or contract stipulations, not from Article 13 itself.
In disputes over whether “one month” means 30 days or a calendar month, Article 13 is the principal statutory anchor unless a more specific governing rule clearly applies.