Introduction
Converting a month number (1-12) to its name ("January"-"December") is a common task across programming languages. Every major language provides built-in date/time libraries that handle this conversion, including locale-aware formatting for internationalization. You can also use simple array lookups for performance-critical code. The key choice is between using a date library (which handles locales and abbreviations) versus a hardcoded array (which is faster but only works for one language).
Python
1import calendar
2import datetime
3
4# Using calendar module
5print(calendar.month_name[1]) # January
6print(calendar.month_name[12]) # December
7print(calendar.month_abbr[1]) # Jan
8
9# Using datetime
10date = datetime.date(2025, 3, 1)
11print(date.strftime("%B")) # March (full name)
12print(date.strftime("%b")) # Mar (abbreviated)
13
14# List all month names
15print(list(calendar.month_name[1:]))
16# ['January', 'February', ..., 'December']
17
18# Locale-aware formatting
19import locale
20locale.setlocale(locale.LC_TIME, "fr_FR.UTF-8")
21print(calendar.month_name[3]) # mars (French)
JavaScript
1// Using Date object and toLocaleString
2function getMonthName(monthNumber) {
3 const date = new Date(2025, monthNumber - 1, 1); // Month is 0-indexed
4 return date.toLocaleString('en-US', { month: 'long' });
5}
6
7console.log(getMonthName(1)); // January
8console.log(getMonthName(12)); // December
9
10// Abbreviated
11function getMonthAbbr(monthNumber) {
12 return new Date(2025, monthNumber - 1, 1)
13 .toLocaleString('en-US', { month: 'short' });
14}
15
16console.log(getMonthAbbr(3)); // Mar
17
18// Locale-aware
19console.log(new Date(2025, 2, 1).toLocaleString('de-DE', { month: 'long' }));
20// März (German)
21
22// Array lookup (fastest)
23const MONTHS = [
24 '', 'January', 'February', 'March', 'April', 'May', 'June',
25 'July', 'August', 'September', 'October', 'November', 'December'
26];
27console.log(MONTHS[5]); // May
Java
1import java.time.Month;
2import java.time.format.TextStyle;
3import java.util.Locale;
4
5// Java 8+ — Month enum
6Month month = Month.of(3);
7System.out.println(month.getDisplayName(TextStyle.FULL, Locale.ENGLISH)); // March
8System.out.println(month.getDisplayName(TextStyle.SHORT, Locale.ENGLISH)); // Mar
9
10// Locale-aware
11System.out.println(month.getDisplayName(TextStyle.FULL, Locale.FRENCH)); // mars
12
13// All months
14for (int i = 1; i <= 12; i++) {
15 System.out.println(Month.of(i).getDisplayName(TextStyle.FULL, Locale.ENGLISH));
16}
C#
1using System;
2using System.Globalization;
3
4// Using CultureInfo
5string monthName = CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(3);
6Console.WriteLine(monthName); // March
7
8// Abbreviated
9string abbr = CultureInfo.CurrentCulture.DateTimeFormat.GetAbbreviatedMonthName(3);
10Console.WriteLine(abbr); // Mar
11
12// Using DateTime
13DateTime date = new DateTime(2025, 3, 1);
14Console.WriteLine(date.ToString("MMMM")); // March
15Console.WriteLine(date.ToString("MMM")); // Mar
16
17// Locale-aware
18CultureInfo french = new CultureInfo("fr-FR");
19Console.WriteLine(french.DateTimeFormat.GetMonthName(3)); // mars
SQL
1-- MySQL
2SELECT MONTHNAME('2025-03-15'); -- March
3SELECT DATE_FORMAT('2025-03-15', '%M'); -- March
4
5-- PostgreSQL
6SELECT TO_CHAR(DATE '2025-03-15', 'Month'); -- March
7SELECT TO_CHAR(DATE '2025-03-15', 'Mon'); -- Mar
8
9-- SQL Server
10SELECT DATENAME(MONTH, '2025-03-15'); -- March
11SELECT FORMAT(CAST('2025-03-15' AS DATE), 'MMMM'); -- March
Common Pitfalls
Off-by-one errors with 0-indexed months: JavaScript's Date constructor uses 0-indexed months (0 = January, 11 = December), but most other languages use 1-indexed (1 = January). Passing month number 3 to JavaScript new Date(2025, 3, 1) gives April, not March. Subtract 1 when constructing JavaScript dates.
Not validating input range: Passing 0 or 13 to month conversion functions causes different behavior depending on the language — some throw exceptions, some wrap around, some return empty strings. Always validate that the month number is between 1 and 12 before converting.
Ignoring locale settings: Hardcoded English month names break for international users. Use locale-aware APIs (toLocaleString in JS, TextStyle with Locale in Java, CultureInfo in C#) when the output is user-facing.
Calendar module indexing in Python: calendar.month_name is a 13-element array where index 0 is an empty string. Using calendar.month_name[0] returns "", not January. Index 1 is January.
Performance in tight loops: Creating Date/DateTime objects inside a loop solely to get month names is wasteful. For performance-critical code, use a static array lookup: MONTHS[monthNumber] is O(1) with no object allocation.
Summary
Python: calendar.month_name[n] or datetime.strftime("%B")
JavaScript: new Date(year, n-1, 1).toLocaleString('en', {month: 'long'})
Java: Month.of(n).getDisplayName(TextStyle.FULL, Locale.ENGLISH)
C#: CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(n)
Use locale-aware APIs for internationalized applications
Use array lookup for maximum performance
