〜おきに — The Gap Logic (Intervals)
Expresses regular intervals between repeated occurrences — "every [other] [unit]" or "at every [distance]." It focuses on the empty gap between occurrences.
Structure
[Number + Unit] + おきに
Examples
3時間おきに薬を飲んでください。
Sanjikan oki ni kusuri wo nonde kudasai.
Please take medicine every 3 hours (with 3-hour gaps).
3時間 (interval) + おきに
電柱は50メートルおきに立っています。
Denchuu wa gojuu meetoru oki ni tatte imasu.
Utility poles stand every 50 meters.
50m (physical interval) + おきに
一日おきに宿題が出る。
Ichinichi oki ni shukudai ga deru.
Homework is assigned every other day.
一日おきに = a one-day gap (Mon, Wed, Fri...)
• Gap vs Count: 3時間おきに means there is a 3-hour GAP between events. 3時間ごとに means 'at each 3-hour mark'. • Common Trap: 一日おき is 'every other day' because the gap is one full day. 二日おき is 'every third day'. • Note: Used for both time and physical distance (meters, steps).
Commonly confused with
The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones 〜おきに is tested against.
vs ごとに
ごとに means 'at each' point (every 3rd hour hits the mark); おきに emphasizes the GAP between, so 一日おき = every OTHER day.
vs 毎〜 (毎日/毎週)
毎 means 'every single' unit without gaps (毎日 = every day); おきに inserts a skipped interval between occurrences.
More time expressions
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