MONTH

What it does

MONTH(serial_number)

MONTH projects a date serial onto its month-of-year component: it discards the fractional part, maps ⌊serial⌋ to a calendar day under the workbook's date system (see FUNC.DATE), and returns that day's month as an integer from 1 (January) to 12 (December).

There is no month arithmetic here and no locale sensitivity: the result is a number, never a month name. Producing "January" is the TEXT function's job, and it is locale-dependent where MONTH is not.

Arguments

MONTH(serial_number) — one required argument, the date whose month is wanted.

Microsoft's guidance for the whole category applies: supply the date as a serial — from DATE, from another formula, or from a cell that already holds a date — rather than as text, because text dates depend on the locale's date order and can be misread. Coercion of the argument follows the ordinary scalar rules in coercion and lifting.

Try it

Quirks

Result and edge cases

Returns a Number in 1…12.

• Fractional serials are floored; the time of day is irrelevant.
• The phantom days. Serial 0 ("0 January 1900") and serial 60 (the non-existent 29 February 1900) both live inside months that do exist, so MONTH returns an unremarkable 1 and 2 respectively under any consistent reading. MONTH is therefore the least diagnostic member of the decomposition trio for the leap-year artefact — but it is also the one whose neighbours reveal it: MONTH(59), MONTH(60) and MONTH(61) should read 2, 2, 3.
• Out-of-range serials. Negative serials are the documented #NUM! case. The upper end is discussed under "What has not been checked".

Errors

As documented for this category:

• #NUM! when serial_number is out of range for the workbook's date-base value.
• #VALUE! when the argument will not convert to a number — the ordinary coercion outcome rather than a rule specific to MONTH.
• An error argument propagates.

How to implement

Notes for implementers

1. Floor before mapping, for the same reason as YEAR: truncation and flooring disagree precisely in the region the range check is meant to reject.
2. Never format inside the kernel. The month number is the value; month names belong to the presentation layer and to TEXT.

Rust code

4 month_fn "MONTH" (1, 1) [V "serial_number"] |s, a, sv| {
    of_date(s, a, |x| k::serial_to_ymd(x).map(|(_, m, _)| m as f64))
}

No implementation has been published with a Handbook test suite for this function.

Version differences

The recorded environments below distinguish a reading from a same-input comparison. Counts describe captured inputs in each environment; overlapping captures and comparisons are not totals of unique worksheet calls.

The record contains no same-input comparison between these environments. Reading different inputs on different builds does not establish either a version change or cross-build agreement.

Recorded environments and comparison details.

Alternatives

Relationships

• YEAR, DAY — the other two projections; together they invert DATE.
• EOMONTH — the natural companion when the question is "the end of this month". DATE(YEAR(s), MONTH(s)+1, 0) is the classic hand-rolled equivalent, and relies on DATE's day-0 rollover rather than on MONTH itself.
• EDATE — month offsetting, which is a different operation from month extraction and is frequently confused with MONTH-based arithmetic. DATE(YEAR(s), MONTH(s)+1, DAY(s)) and EDATE(s,1) are believed to disagree at end-of-month — the former rolls 31 January into 3 March by DATE's documented day carry, while EDATE is generally understood to clamp. EDATE's Microsoft page does not state the clamping rule, and this Handbook has not verified it.
• DATEDIF with unit "M" — complete months between two dates, which is not a difference of MONTH values.

Named variants

No named variants are recorded yet.