ごとに— Every / Each / At each

• 3時間ごとに薬を飲んでください。

  Sanjikan goto ni kusuri o nonde kudasai.

  Please take medicine every 3 hours.

  3時間ごとに = at each 3-hour interval

• 駅ごとに電車が止まります。

  Eki goto ni densha ga tomarimasu.

  The train stops at every station.

  駅ごとに = at each station

• このバスは10分ごとに来ます。

  Kono basu wa juppun goto ni kimasu.

  This bus comes every 10 minutes.

  10分ごとに = at each 10-minute interval

• ・ごとに vs おきに: ごとに = at EACH occurrence/interval (emphasized repetition).
• ・Detail: おきに = with GAPS of that size between events (the interval between events).
• ・Summary: With time, 3時間ごとに and 3時間おきに happen to coincide; but 1日おきに = every OTHER day, while 1日ごとに = every day — so they differ.

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ごとに is tested against.

• 間 (あいだ) — Throughout a Duration
• 間に (あいだに) — A Point Within a Window
• あとで — After (with a time gap)
• 頃 / ごろ — Around / About (approximate time)
• までに — By / No later than (deadline)
• 〜おきに — The Gap Logic (Intervals)
• たばかり — Just did (subjective recency)
• たところ — Just finished (this very moment)