Cron Expression Explainer

Cron Expression Reference

A cron expression is a string with 5 fields separated by spaces. Each field controls a different unit of time for your scheduled job.

Field Positions

Position	Field	Allowed Values	Special Characters
1st	Minute	0–59	* , - /
2nd	Hour	0–23	* , - /
3rd	Day of Month	1–31	* , - / ?
4th	Month	1–12 (or JAN-DEC)	* , - /
5th	Day of Week	0–7 (0 & 7 = Sunday)	* , - /

Special Characters

• * — match any value
• */n — every nth unit (e.g. */5 in minutes = every 5 minutes)
• a-b — range from a to b (e.g. 1-5 in day-of-week = Monday through Friday)
• a,b,c — list of specific values

Common Examples

Expression	Meaning
* * * * *	Every minute
0 * * * *	Every hour, on the hour
0 0 * * *	Every day at midnight
0 9 * * 1-5	9am, weekdays only
*/15 * * * *	Every 15 minutes
0 0 1 * *	First day of each month at midnight
30 6 * * 0	6:30am every Sunday
0 0 * * 0	Weekly, midnight Sunday

Frequently Asked Questions

What is a cron expression?

A cron expression is a schedule string used to trigger recurring tasks. It was invented for Unix cron daemons and is now universally used in cloud schedulers (AWS EventBridge, GitHub Actions, Kubernetes CronJobs, crontab, etc.).

Why does my cron expression not run when I expect?

The most common issues: (1) timezone — most cron systems run in UTC by default, not your local time; (2) field order — minute comes first, not hour; (3) 0 and 7 both mean Sunday in day-of-week.

What is the difference between day-of-month and day-of-week?

If you specify both, most cron implementations use an OR — the job runs if either condition matches. To target "first Monday of the month" you need a workaround, since standard cron can't express that directly.