ごとに

Particle (Basic ㊦ 128)

Something takes place regularly in succession after a certain temporal or spatial interval.

Equivalent: Every

私は三時間ごとに薬を飲んだ・飲みました。: I took medicine every three hours.
正月は家ごとに門松を立てる・立てます。: They put up pine tree decorations at every house on New Year's Day.
一課ごとに試験がある。: There is a test after every lesson.
学期ごとに先生が変わる。: Every semester teachers change.
木村さんは会う人ごとに挨拶している。: Mr. Kimura greets everyone he meets.
三日ごとにテニスをしています。: I'm playing tennis every third day.

Notes

【Related Expression】

おきに indicates that something is repeated at certain intervals. Although its usage is comparable to ごとに, note the distinct difference in meanings in examples [1a] and [1b].

[1]

a. この電車はニ駅おきに止まる。
This train stops at every third station.

b. この電車はニ駅ごとに止まる。
This train stops at every other station.

When a time expression precedes おきに or ごとに, there is no difference in meaning, if an event takes place at one point in time as in [2a]. But there is difference in meaning, if an event takes place within a certain period of time as in [2b].

[2]

a. 電車は五分おきに/ごとに出る。
The train leaves every five minutes.

b. 私は二日おきに/ごとに花子と会っている。
I'm seeing Hanako every third day/every other day.