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Cron every 4 hours

The cron expression for every 4 hours is 0 */4 * * *, running six times a day at 0, 4, 8, 12, 16 and 20 o'clock. Offsets, mistakes, and the GitHub Actions and AWS forms.

Cron expression
0 */4 * * *
See the next run times

The expression

0 */4 * * *

Runs at minute 0 of hours 0, 4, 8, 12, 16 and 20: six times a day. Since 24 divides evenly by 4, every gap is exactly 4 hours, including 20:00 to 00:00.

Field Value Meaning
Minute 0 at minute 0
Hour */4 every 4th hour, starting at 0
Day of month * every day
Month * every month
Day of week * every day of the week

The equivalent list form is 0 0,4,8,12,16,20 * * *. The step is anchored to midnight, not to when you installed the job.

Variants

Schedule Expression
Every 4 hours from 2:00 (2, 6, 10, 14, 18, 22) 0 2-23/4 * * *
Every 4 hours from 1:00 (1, 5, 9, 13, 17, 21) 0 1-23/4 * * *
Every 4 hours at 30 past 30 */4 * * *
Every 4 hours during the day (8, 12, 16, 20) 0 8-20/4 * * *
Every 4 hours on weekdays 0 */4 * * 1-5
Every 3 hours 0 */3 * * *
Every 6 hours 0 */6 * * *
Every 12 hours 0 */12 * * *

An offset like 2-23/4 is handy when other jobs already run at midnight: the 4-hour cadence stays the same, but the heavy work moves away from 00:00.

Where to write it

  • crontab (Linux, macOS): 0 */4 * * * /usr/local/bin/refresh-cache.sh in crontab -e. Hours are in the server's time zone; check it with timedatectl or date.
  • GitHub Actions: on: schedule: - cron: '0 */4 * * *'. Always UTC. GitHub warns that the start of every hour is a high-load time, so 13 */4 * * * is less likely to be delayed.
  • Kubernetes CronJob: schedule: "0 */4 * * *", plus timeZone: "Asia/Tokyo" (or yours) to run on local hours.
  • AWS EventBridge: cron(0 0/4 * * ? *) in six fields with ? for day of week, or rate(4 hours), counted from when the rule was created.

Common mistakes

  • 0 4 * * * is once a day, at 04:00. Without the slash it's a single hour.
  • */4 * * * * runs every 4 minutes, 360 times a day.
  • Forgetting the minute. * */4 * * * runs every minute for the whole hour, six times a day.
  • Time zone surprises. "Every 4 hours from midnight" on a UTC host is not midnight locally. Convert, or set timeZone/CRON_TZ.

Paste any expression into the Cron Expression Parser to see it in words and its next run times.