Cron Expression Examples

How to read the five fields

A crontab line is five whitespace-separated fields followed by the command to run. Reading left to right, the fields get coarser: minute, hour, day of month, month, day of week.

* * * * *  command-to-run
| | | | |
| | | | +--- day of week   (0-7, 0 and 7 are Sunday)
| | | +----- month         (1-12, or JAN-DEC)
| | +------- day of month  (1-31)
| +--------- hour          (0-23)
+----------- minute        (0-59)

Four operators work in every field. An asterisk means every value. A comma builds a list (1,15). A hyphen builds a range (9-17). A slash adds a step, either to the whole field (*/5) or inside a range (8-18/2).

Every few minutes

The most looked-up schedules of all. One hard limit worth knowing up front: standard cron checks its table once a minute, so a minute is the shortest interval you can express. There is no way to write "every 30 seconds".

Every few hours

Put a fixed minute in the first field, then step the hour field. Leaving the minute as an asterisk here is a common accident: 0 */2 * * * runs twice a day at the top of the hour, while * */2 * * * runs 720 times a day.

Once or twice a day

Both the minute and the hour are pinned, so the job fires exactly once per matching day. These are the schedules for backups, report generation, cache warming and nightly imports.

Specific days of the week

The fifth field takes 0-7 or the three-letter English names SUN, MON, TUE, WED, THU, FRI and SAT. Because both 0 and 7 map to Sunday, a range like 1-5 is Monday through Friday and 6,0 is the weekend.

Days of the month, months and years

Once you restrict the day-of-month or month fields, the job can fire as rarely as once a year. Watch the short months: an expression pinned to the 31st simply does not run in the five months that end on the 30th, and February drops two more.

The @ shortcuts

Most cron implementations accept a handful of named shortcuts in place of the five fields. They are just aliases, so anything you can do with them you can also write out longhand.

There is one more, @reboot, which runs the job once after the machine starts. It is deliberately missing from the table above because it is not a schedule at all — it has no next run time, so nothing can predict when it will fire.

Expressions that do not mean what they look like

These are all valid, and all of them regularly get written by someone expecting different behavior. The descriptions below are what actually happens.

Three rules that explain most cron bugs

1. A step counts from the start of the field, not from now. */45 does not mean "every 45 minutes" — it means minutes 0 and 45 of every hour, and the gap between the second run and the next is 15 minutes, not 45. The same applies to */7 in the hour field, which resets at midnight.
2. When both the day-of-month and the day-of-week fields are restricted, cron runs the job when either one matches, not both. The crontab manual is explicit about this: "the command will be run when either field matches the current time." If only one of the two is restricted, the other being * means it is ignored and the behavior is the intuitive one.
3. Cron uses the clock of the machine it runs on, and that is very often UTC even when you are not. A schedule that reads 03:00 to you may be running mid-afternoon on the server, so always confirm the host timezone before trusting an overnight window.

One more absence to plan around: standard Unix cron has no "last day of the month" syntax. The usual workaround is to schedule the job on the 28th, or to run it daily and let the command itself exit early unless tomorrow is the 1st. The L, W and # characters you may have seen belong to Quartz, a different scheduler with a six or seven field expression that starts with seconds.

Checking your own expression

A table can only cover the schedules people ask for most. When you have an expression that is not on this page — or you have edited one of these and want to be sure — paste it into the cron expression parser on this site. It names each field, turns the whole line into a sentence, previews the next five run times in your local timezone, and tells you which field is invalid when the expression will not parse at all. It runs entirely in your browser, so nothing you paste is uploaded anywhere.