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Cron twice a day

A cron expression for twice a day is 0 9,21 * * *, at 9:00 and 21:00. How lists work, how to pick other times or minutes, and the GitHub Actions and AWS forms.

Cron expression
0 9,21 * * *
See the next run times

The expression

0 9,21 * * *

Runs at 09:00 and 21:00 every day: twice a day, 12 hours apart.

Field Value Meaning
Minute 0 at minute 0
Hour 9,21 at 9 a.m. and 9 p.m.
Day of month * every day
Month * every month
Day of week * every day of the week

A comma makes a list: the field matches any of the values. Any two hours work, and they don't have to be 12 hours apart: 0 8,17 * * * runs at 8:00 and 17:00. Every value in the hour list shares the same minute, though.

Variants

Schedule Expression
Midnight and noon 0 0,12 * * *
6:00 and 18:00 0 6,18 * * *
8:00 and 17:00 on weekdays 0 8,17 * * 1-5
8:30 and 17:00 (different minutes) two lines: 30 8 * * * and 0 17 * * *
Three times a day (8, 14, 20) 0 8,14,20 * * *
Once a day at 9:00 0 9 * * *
Every 6 hours 0 */6 * * *

When the two times need different minutes, cron can't combine them in one line: 30,0 8,17 * * * would run four times (8:00, 8:30, 17:00, 17:30), because every minute in the list pairs with every hour. Write two entries instead.

Where to write it

  • crontab (Linux, macOS): 0 9,21 * * * /usr/local/bin/sync.sh in crontab -e, in the server's time zone.
  • GitHub Actions: on: schedule: - cron: '0 9,21 * * *' means 09:00 and 21:00 UTC. To get local times, convert each hour (for Berlin in summer, UTC+2, that's 0 7,19 * * *). For two different minutes, GitHub accepts several - cron: entries under schedule:.
  • Kubernetes CronJob: schedule: "0 9,21 * * *" with timeZone: for local hours. One CronJob holds one schedule, so different minutes need two CronJobs.
  • AWS EventBridge: cron(0 9,21 * * ? *), six fields with ? in day of week. EventBridge rules are UTC; EventBridge Scheduler can take a time zone.

Common mistakes

  • 0 9-21 * * * is every hour from 9:00 to 21:00, 13 runs. A dash is a range; a comma is a list.
  • 0,30 9 * * * runs at 9:00 and 9:30, twice in the same hour, not twice a day.
  • Spaces in the list. 0 9, 21 * * * has six fields and is rejected or misread. Lists never contain spaces.
  • Assuming the second run is 12 hours after the first finished. Cron is clock-based; a long 9:00 run doesn't move the 21:00 one.

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