Japanese Numbers, Dates, and Time Expressions

Mastering numbers, dates, and time is the gateway to practical, daily communication in Japanese. It allows you to schedule appointments, understand prices, discuss age, and navigate the calendar—essential skills that move you from memorizing vocabulary to engaging with the real world. This system has its own logic and unique features, such as counters and specific calendar conventions, which are crucial to learn correctly from the start.

Foundational Number Systems: On-yomi and Kun-yomi

Japanese numerals are built upon two primary reading systems: on-yomi (Sino-Japanese readings) and kun-yomi (native Japanese readings). Knowing which to use is your first critical step. The on-yomi readings are derived from Chinese and are typically used in most number-based constructions, especially for counting in the abstract, for telephone numbers, and in mathematics. The basic set from one to ten is: ichi (1), ni (2), san (3), shi/yon (4), go (5), roku (6), shichi/nana (7), hachi (8), kyuu/ku (9), juu (10).

The kun-yomi readings are the native Japanese words and are used in a smaller set of contexts, most notably for counting up to ten items in a general sense (hitotsu, futatsu, mittsu, etc.) and in some traditional or formal phrases. A learner's key insight is that on-yomi forms the backbone of the numerical system, allowing you to create larger numbers logically. For example, 11 is juu-ichi (10 + 1), 20 is ni-juu (2 x 10), and 365 is $san-byaku-roku-juu-go$. Pay attention to sound changes: 300 is $san-byaku$ (not $san-hyaku$), and 600 is $roppyaku$.

The World of Counters and Irregular Pronunciations

Numbers rarely stand alone; they are almost always attached to a counter suffix that specifies what is being counted. This is where the system becomes both precise and challenging. Different objects require different counters: -hon for long cylindrical objects (bottles, pencils), -mai for flat objects (paper, shirts), -dai for machines (cars, computers), and -nin or -hito for people.

The major hurdle is that the numbers themselves often change pronunciation when combined with certain counters. These are not random; they follow patterns of sound mutation for ease of speech. For example, the number one (ichi) becomes ip- before the counter -pon (for bottles), giving you ippon. Three (san) becomes sam- before -bai (for cupfuls), giving sambai. You must memorize the most common counters and their associated number irregularities. A critical trio to start with involves the generic item counter -tsu (using kun-yomi: hitotsu, futatsu...), the people counter -nin (hitori, futari, $san-nin$...), and the general-purpose -ko for small, compact items (ikko, niko, $sanko$...).

Expressing Dates: Order and Calendar Vocabulary

Dates in Japanese follow a logical year-month-day-weekday order, which is the reverse of the common American format but aligns with an expanding sequence. The year is said first, then the month, then the day. Years can be expressed in the Western Gregorian calendar ($2025-nen$) or, formally, in the Japanese era name system, such as $Reiwa7-nen$.

Months are beautifully simple: they are the numbers 1 through 12 followed by -gatsu. January is ichi-gatsu, February is ni-gatsu, and so on. Days of the month, however, are less regular. While the 1st through the 10th, plus the 14th, 20th, and 24th, have unique names (e.g., 1st: tsuitachi; 2nd: futsuka), most other days are formed by the number + -nichi (11th: $juu-ichi-nichi$). You must memorize the first ten and the special -ka endings. Days of the week end in -youbi (nichiyoubi = Sunday, getsuyoubi = Monday). A full date is read aloud as, for example, $Reiwa7-nensangatsufutsukanodoyoubi$ (Saturday, March 2nd, Reiwa 7).

Telling Time and Expressing Duration

Telling time combines the hour and minute. The hour is expressed with the number followed by -ji (時). The minute is the number followed by -fun (分), which also has pronunciation irregularities. Four o'clock is $yo-ji$ (not $yon-ji$ or $shi-ji$). For minutes, note: 1 min = $ip-pun$, 3 min = $san-pun$, 4 min = $yon-pun$, 6 min = $rop-pun$, 8 min = $hap-pun$, and 10 min = $jup-pun$. To say "4:08," you would say $yo-jihap-pun$.

To discuss duration—how long something takes—you change the suffix. Hour duration uses -jikan (時間), and minute duration uses -funkan (分間). The key difference is between $san-ji$ (3 o'clock) and $san-jikan$ (three hours). Duration for days uses -kakan (日間) or the special -nichikan, and for months, $\ast -kagetsu-kan$ (ヶ月間). Mastering these duration markers is essential for scheduling and describing activities.

Common Pitfalls

1. Misapplying Number Readings: Using yon (4) or nana (7) when the counter demands shi or shichi. For instance, the month April is $shi-gatsu$, never $yon-gatsu$. Conversely, for generic counting, yon and nana are more common. Rule of thumb: use yon and nana unless you've specifically learned a counter requires the other form.
2. Confusing Time Point vs. Duration: Saying $ni-jikan$ when you mean $ni-ji$. This changes "two hours" into "two o'clock." Always double-check whether you are stating a point in time ($-ji$, $-nichi$) or a span of time ($-jikan$, $-nichikan$).
3. Overlooking Counter Irregularities: Applying the standard ichi, ni, san to all counters. This will sound immediately unnatural. Drill the sound changes for high-frequency counters like -hon, -mai, and -hiki (for small animals) through repetition and flashcards.
4. Mixing Up Calendar Terms: Applying the regular number pattern to the first ten days of the month. The 1st is not $ichi-nichi$ but tsuitachi. Trying to use the regular pattern here is a very common early mistake that will confuse listeners.

Summary

• Japanese uses on-yomi number readings as the foundation for creating complex numbers and for most practical counting situations, while kun-yomi appears in specific, often traditional, contexts.
• Counters are mandatory and often trigger predictable but must-know irregularities in number pronunciation (e.g., ippon, $sanbon$).
• Dates follow a year-month-day-weekday order. Months are regular (-gatsu), but days of the month require memorization of the unique names for the first ten days and certain others.
• Telling time requires knowing the irregular pronunciations for minutes ($-fun/pun$). Crucially, you must distinguish between a point in time (e.g., $-ji$) and a duration of time (e.g., $-jikan$).
• Understanding the Japanese era name system for years and the specific vocabulary for weeks, months, and calendar terms is essential for navigating appointments and formal documents.