Dev Basics · 5 min read
Understanding Cron Syntax (With Examples)
Cron is the classic way to run tasks on a schedule on Unix systems, and its syntax powers everything from backups to newsletter sends. The five-field format looks cryptic at first but is simple once you see the pattern.
This guide walks through each field, the special characters, and practical examples you can adapt.
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The five fields
A standard cron expression has five fields, in order: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–6, where 0 is Sunday). A job runs when the current time matches all the fields.
For example, 30 9 * * 1 means "at 9:30, on any day of the month, in any month, but only on Monday."
The special characters
An asterisk * means "every" value for that field. A slash defines steps: */15 in the minute field means every 15 minutes. Commas list values: 0,30 means at :00 and :30. A hyphen sets a range: 9-17 means from 9 through 17.
Common schedules
Every 15 minutes: */15 * * * *. Every day at midnight: 0 0 * * *. Every weekday at 8am: 0 8 * * 1-5. On the first of every month: 0 0 1 * *. Every Sunday at 3am: 0 3 * * 0.
Watch out for timezones
Cron runs in the server's local timezone unless configured otherwise. A job scheduled for "midnight" runs at midnight wherever the server thinks it is — a frequent source of surprise. Always confirm the timezone your scheduler uses.