Every…: 〜おきに・〜ごとに

〜おきに and 〜ごとに both translate “every…”. ごとに counts each unit: 一日ごとに = every day. おきに skips units: 一日おきに = leaving a day's gap, i.e. every other day. With minutes, hours or distances, the difference often disappears: 十分おきに and 十分ごとに both mean “every ten minutes”.

• このバスは十分おきに来ます。このばすはじゅっぷんおきにきます。This bus comes every ten minutes.
• この薬は一日おきに飲んでください。このくすりはいちにちおきにのんでください。Please take this medicine every other day.
• 季節ごとに、京都の庭は表情を変える。きせつごとに、きょうとのにわはひょうじょうをかえる。With each season, Kyoto's gardens take on a new look.

おく means “to leave, to put”: 一日おきに is “leaving one (empty) day in between”. ごと means “each”: 一日ごとに is “on each day”. For units you count like boxes (days, weeks, months, years, floors), the difference is clear-cut — English “every other day” versus “every day”.

• この雑誌は、一か月おきに出る。このざっしは、いっかげつおきにでる。This magazine comes out every two months.
• 大会は四年ごとに開かれる。たいかいはよねんごとにひらかれる。The tournament is held every four years.

For days, weeks, years: N おきに = every N+1. For fine units of time (minutes, hours) and distances (metres), you think in intervals and the two forms converge: 十分おきに = 十分ごとに = every ten minutes.

• ゴミは一週間おきに出す。ごみはいっしゅうかんおきにだす。This kind of rubbish goes out every other week.
• 一時間ごとに、お寺の鐘が鳴る。いちじかんごとに、おてらのかねがなる。The temple bell rings every hour.

ごとに also attaches to a noun with no number: 人ごとに (for each person), 国ごとに (for each country), 季節ごとに (with each season). It says the thing varies or recurs unit by unit. おきに isn't used this way: it always needs a number.

• 考え方は人ごとに違う。かんがえかたはひとごとにちがう。Ways of thinking differ from person to person.