Cron Atlas

Cron expression for every 45 minutes

0,45 */3 * * *
30 1-23/3 * * *
15 2-23/3 * * *

Every 45 minutes, counted from midnight.

Next 10 runs

In Cron, worked out in your browser from the current time.

At a glance

Runs
32 a day
Gap between runs
Always 45 minutes
Expressible in
All six dialects
Clock changes
Affected in New York, London, Berlin, Helsinki, Sydney

Open in the tester

In each dialect

Every expression here is generated by the tester’s own engine and checked run for run against the others, so “Exact” means the same clock times in the same zone. Each one links to the tester.

Cron
0,45 */3 * * *and30 1-23/3 * * *and15 2-23/3 * * *
0,45 */3 * * * /path/to/command
30 1-23/3 * * * /path/to/command
15 2-23/3 * * * /path/to/command
  • Add all 3 lines to the crontab.
Needs 3 schedules
EventBridge
0,45 0/3 * * ? *and30 1/3 * * ? *and15 2/3 * * ? *
aws events put-rule --name every-45-minutes --schedule-expression "cron(0,45 0/3 * * ? *)"
aws events put-rule --name every-45-minutes --schedule-expression "cron(30 1/3 * * ? *)"
aws events put-rule --name every-45-minutes --schedule-expression "cron(15 2/3 * * ? *)"
  • Wrap it in cron(…). Day of week is ? because day of month already holds *, and a * in both is rejected. The final * is the required year field.
  • Create one rule per expression, each with the same target. A single rate(45 minutes) also works, but it counts from when the rule is created, not from midnight.
Needs 3 schedules
Quartz
0 0,45 0/3 * * ?and0 30 1/3 * * ?and0 15 2/3 * * ?
CronScheduleBuilder.cronSchedule("0 0,45 0/3 * * ?")
CronScheduleBuilder.cronSchedule("0 30 1/3 * * ?")
CronScheduleBuilder.cronSchedule("0 15 2/3 * * ?")
  • The leading 0 is the seconds field, so it fires at the top of the minute. Day of week is ? because day of month already holds *, and a * in both is rejected. The optional year is left off.
  • Attach one CronTrigger per expression to the same job. SimpleScheduleBuilder.repeatMinutelyForever(45) is the one-trigger alternative, counted from the trigger’s start time.
Needs 3 schedules
Kubernetes
0,45 */3 * * *and30 1-23/3 * * *and15 2-23/3 * * *
schedule: "0,45 */3 * * *"
schedule: "30 1-23/3 * * *"
schedule: "15 2-23/3 * * *"
  • A CronJob takes one schedule, so this needs 3 CronJobs sharing a job template.
  • If a Job can run longer than 45 minutes, the next one starts alongside it by default. concurrencyPolicy: Forbid skips the new run instead, and Replace stops the old one.
  • The controller stops starting a CronJob that has missed more than 100 schedules. At this rate that is 75 hours of downtime. startingDeadlineSeconds limits how far back it counts.
Needs 3 schedules
GitHub
0,45 */3 * * *and30 1-23/3 * * *and15 2-23/3 * * *
- cron: '0,45 */3 * * *'
- cron: '30 1-23/3 * * *'
- cron: '15 2-23/3 * * *'
  • GitHub warns that schedules can be delayed at high load, which includes the start of every hour, and that some queued jobs may be dropped. A different minute reduces the risk.
  • List all 3 under schedule: in one workflow. github.event.schedule tells a step which one fired.
Needs 3 schedules
Azure
0 0,45 */3 * * *and0 30 1/3 * * *and0 15 2/3 * * *
[TimerTrigger("0 0,45 */3 * * *")]
[TimerTrigger("0 30 1/3 * * *")]
[TimerTrigger("0 15 2/3 * * *")]
  • Six fields with seconds first, so the leading 0 fires at the top of the minute.
  • A timer trigger takes one expression, so this needs 3 functions. On an App Service plan, the TimeSpan 00:45:00 is the single-trigger alternative, measured between runs rather than from midnight.
Needs 3 schedules

About this schedule

The obvious */45 is a trap: in the minute field it means minutes 0 and 45, so runs come 45 minutes apart and then 15. A true 45-minute cycle repeats every three hours (00:00, 00:45, 01:30, 02:15, 03:00), so cron needs three lines, one for each position in that cycle. Because 45 minutes divides a day exactly, the pattern restarts cleanly at midnight.

Clock changes

Worked out by running each dialect’s engine through New York’s clock changes; it is affected in London, Berlin, Helsinki, Sydney too, at their own local hours.

DialectClocks go forward (02:00 becomes 03:00)Clocks go back (02:00 becomes 01:00)
Cron02:15 doesn’t exist that day, so it’s skipped01:30 happens twice, and it runs both times
EventBridge Scheduler02:15 doesn’t exist that day, so it’s skipped01:30 happens twice, and it runs once, in the first pass
Quartz02:15 doesn’t exist that day, so it’s skipped01:30 happens twice, and it runs once, in the second pass
Kubernetes02:15 doesn’t exist that day, so it’s skipped01:30 happens twice, and it runs both times
GitHub02:15 doesn’t exist that day. GitHub moves it to 03:00, where it is counted once with the 03:00 run01:30 happens twice. GitHub doesn’t document whether it repeats; shown once here
Azure02:15 doesn’t exist that day, so it runs at 03:1501:30 happens twice, and it runs both times

Cron follows the crontab man page; daemons differ, and cronie catches up skipped fixed-time jobs. EventBridge applies to Scheduler with a time zone; scheduled rules run in UTC and never see a clock change. Quartz is exact for 2.5.2. GitHub documents the forward case only.

Questions

What is the cron expression for every 45 minutes?
It takes 3 lines, used together: 0,45 */3 * * *, 30 1-23/3 * * *, 15 2-23/3 * * * in standard cron, Kubernetes and GitHub Actions. The other dialects differ: 0,45 0/3 * * ? *, 30 1/3 * * ? *, 15 2/3 * * ? * in EventBridge; 0 0,45 0/3 * * ?, 0 30 1/3 * * ?, 0 15 2/3 * * ? in Quartz; 0 0,45 */3 * * *, 0 30 1/3 * * *, 0 15 2/3 * * * in Azure.
Why doesn’t */45 run every 45 minutes?
A step only counts within one field and restarts each hour. In the minute field, */45 is minutes 0 and 45, so the gaps alternate between 45 and 15 minutes. The three lines on this page give a steady 45-minute gap.
What happens to this schedule when the clocks change?
It depends on the scheduler. When clocks go forward in New York (02:00 becomes 03:00): Cron, EventBridge, Quartz and Kubernetes: 02:15 doesn’t exist that day, so it’s skipped. GitHub: 02:15 doesn’t exist that day. GitHub moves it to 03:00, where it is counted once with the 03:00 run. Azure: 02:15 doesn’t exist that day, so it runs at 03:15. The table on this page also covers the autumn change.

More schedules