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Cron Expression Explainer & Next Run Calculator
Decode any 5-field cron expression and see its next scheduled run times.
About this tool
Cron expressions are compact, but they are easy to get wrong: a single misplaced asterisk can turn a nightly backup into a job that fires every minute. This tool parses a standard five-field cron expression (minute, hour, day of month, month, day of week), explains what each field matches, and calculates the next five times the schedule will actually fire in your local time zone.
It supports wildcards, lists (1,15), ranges (9-17), steps (*/10 and 0-30/5), month and weekday names (JAN, MON-FRI) and the common shortcuts @hourly, @daily, @weekly, @monthly and @yearly. It also follows the classic Vixie-cron rule: when both day-of-month and day-of-week are restricted, the job runs when either matches.
Everything is calculated in your browser, so you can safely test expressions that belong to private servers.
How to use it
- Type or paste a cron expression, or click one of the presets.
- Press Explain.
- Read the field-by-field breakdown and check the upcoming run times match what you intended.
A worked example
Take */15 9-17 * * MON-FRI. The minute field */15 expands to 0, 15, 30 and 45. The hour field 9-17 covers 9 through 17. Day-of-month and month are wildcards, and the weekday field limits it to Monday through Friday. Put together: every quarter hour from 09:00 to 17:45 on weekdays. Note the last run is 17:45, not 17:00, because hour 17 includes all four of its quarter-hours. That is a classic off-by-one in how people read these.
Common mistakes
- Writing
0 */2 * * *and expecting "every two hours from now". It means hours 0, 2, 4... of the clock, not two hours after you saved it. - Using
*/45in the minute field and expecting a 45-minute interval. It runs at minute 0 and 45 of every hour, so the gap alternates between 45 and 15 minutes. - Forgetting that Sunday is 0 (and also 7 in most implementations).
Troubleshooting a job that still does not fire? See our cron debugging checklist.
Frequently asked questions
Does this support seconds or year fields?
No. It targets the standard five-field format used by Linux crontab, most hosting panels and many schedulers. Quartz-style six or seven field expressions are not supported.
Which time zone are the next runs shown in?
Your browser's local time zone. A real server may run in UTC, so convert accordingly before relying on the times.
Why does my day-of-month and weekday combination run more often than expected?
In classic cron, if both fields are restricted the job fires when either one matches, not only when both do.
Results are provided for general information. Please read our disclaimer.