Months in Japanese: readings, IPA and the old names 睦月 to 師走

Why the months in Japanese are numbered

Japanese counts its months where most European languages name them. The word for each month is the Sino-Japanese number followed by 月, read gatsu: ichi plus gatsu gives ichigatsu, January, and jūni plus gatsu gives jūnigatsu, December. Learners who can count to twelve already know the months in Japanese, provided they use the right reading of the number.

The numbering is older than the Western calendar in Japan. The lunisolar calendar used before 1873 also counted its months from one to twelve, but its months followed the Moon and its year began later than 1 January. The Gregorian calendar arrived in 1873 as part of the Meiji reforms, and since 1876, according to the English Wikipedia article on the Japanese calendar, January has officially been the first month. The labels stayed, while the months they label moved by several weeks.

The character 月 has three common readings, and each has its job. Gatsu names a calendar month. Getsu appears in 月曜日 getsuyōbi, Monday, and in the counter for durations. Tsuki is the native word for the Moon and for a month in general, the form the Asian word list gives for month.

April, July and September: three readings to learn

Three of the months in Japanese break the pattern of the modern numbers. When Japanese people count, four is usually yon, seven nana and nine kyū. The months keep the older Sino-Japanese readings instead: 4月 is shigatsu, 7月 shichigatsu and 9月 kugatsu. Wiktionary gives only these readings for the three months and lists no yongatsu or nanagatsu.

The English Wikipedia article on Japanese numerals explains the background. Shi, four, sounds like 死, death, and ku, nine, like 苦, suffering, so everyday counting avoids both. Shichi is avoided for a practical reason: it is easy to confuse with ichi and hachi. Set expressions keep the old forms, and the month names are among the oldest set expressions of all.

Writing dates with the months in Japanese

A Japanese date runs from the largest unit to the smallest: year 年, month 月, day 日. 28 October 2026 is 2026年10月28日, read nisen nijūroku-nen jūgatsu nijūhachi-nichi. Add the weekday in brackets and it becomes 2026年10月28日(水), the long date format that the Unicode CLDR data defines for Japanese. The same data gives 2026/10/28 as the medium numeric format.

Official documents may give the year in the Japanese era system. The current era, 令和 Reiwa, began on 1 May 2019, which was Reiwa 1, written 令和元年 Reiwa gannen. Subtracting 2018 from a Gregorian year since 2019 gives the Reiwa year, so 2026 is 令和8年.

Days of the month follow numbers too, with a set of native readings at the start of the month. The first is 一日 tsuitachi, the second 二日 futsuka, the third 三日 mikka, and so on to the tenth, 十日 tōka. From the eleventh the Sino-Japanese number plus nichi takes over, with three exceptions: the fourteenth 十四日 jūyokka, the twentieth 二十日 hatsuka and the twenty-fourth 二十四日 nijūyokka.

Using the months in Japanese sentences

In a month is the month plus the particle に: 4月に日本へ行きます, I am going to Japan in April. The question is 何月 nangatsu, which month, and the answer has the same shape: 誕生日は何月ですか, which month is your birthday, 8月です, it is August.

Length of time takes a different word. A month as a duration is counted with the counter ヶ月 kagetsu, also written か月 or カ月: 一ヶ月 ikkagetsu is one month, 三ヶ月 sankagetsu three months, and 何ヶ月 nankagetsu asks how many. The two are easy to confuse: 3月 sangatsu is March; 3ヶ月 sankagetsu is a period of three months.

Relative months use 来月 raigetsu, next month, 先月 sengetsu, last month, and 今月 kongetsu, this month. All three read 月 as getsu, the reading of the counter, and none of them needs a particle when it simply says when: 来月引っ越します, I am moving next month.