３０さんじゅう日にち

さ

ん

じゅ

う

に

ち

Meanings

1

30th day of the month

Refers specifically to the 30th calendar day; used in dates like ３月３０日 (March 30th).

The meeting will be held on March 30th.

３０日にちまでに書しょ類るいを提てい出しゅつしてください。

Please submit the documents by the 30th.

2

30 days

Indicates a duration of thirty days; often used with counters or in expressions like ３０日間.

〈事こと〉から３０さんじゅう日にち以い内ないにwithin 30 days of (something happening)
契けい約やく書しょは署しょ名めいから30日にち以い内ないに返へん送そうしてください。
Please return the contract within 30 days of signing.
３０さんじゅう日にち払ばらい30-day payment term
この取とり引ひきは30日にち払ばらいの条じょう件けんで進すすめます。
We'll proceed with this deal on 30-day payment terms.

３１さんじゅういち日にち
３１日 refers to the 31st day (or 31-day span) while ３０日 refers to the 30th day (or 30-day span), and the two are easy to misread or mistype since they differ by only one character.

３０さんじゅう日にち
Standard modern spelling using Arabic numerals; very common in dates and durations.
三さん十じゅう日にち
Kanji spelling; equally common and often used in formal or vertical writing.
三〇日さんじゅうにち
Uses the kanji zero 〇; occasionally seen in official documents or ledgers, but less common in everyday text.

Compound of 三十 (さんじゅう, 'thirty') + 日 (にち, 'day'). The reading にち is the standard on'yomi for 日 when used in day counters.