Cron Expressions Explained: Syntax, Examples, and Common Schedules

What is a Cron Expression?

A cron expression is a string of five (or six) fields that defines a schedule for recurring tasks. Originally from Unix cron jobs, the format is now used everywhere: GitHub Actions, AWS CloudWatch, Kubernetes CronJobs, CI/CD pipelines, and task schedulers.

Cron Syntax

A standard cron expression has five fields:

┌───────────── minute (0-59)
│ ┌───────────── hour (0-23)
│ │ ┌───────────── day of month (1-31)
│ │ │ ┌───────────── month (1-12)
│ │ │ │ ┌───────────── day of week (0-7, 0 and 7 = Sunday)
│ │ │ │ │
* * * * *

Special Characters

Character	Meaning	Example
*	Any value	* * * * * = every minute
,	List of values	1,15 * * * * = minute 1 and 15
-	Range	1-5 * * * * = minutes 1 through 5
/	Step	*/5 * * * * = every 5 minutes

Common Cron Schedules

Schedule	Expression	Description
Every minute	* * * * *	Runs 1,440 times/day
Every 5 minutes	*/5 * * * *	Runs 288 times/day
Every 15 minutes	*/15 * * * *	Runs 96 times/day
Every 30 minutes	*/30 * * * *	Runs 48 times/day
Every hour	0 * * * *	At minute 0 of every hour
Every 2 hours	0 */2 * * *	At minute 0, every 2 hours
Every day at midnight	0 0 * * *	Once per day at 00:00
Every day at noon	0 12 * * *	Once per day at 12:00
Every day at 9am	0 9 * * *	Once per day at 09:00
Every Monday at 9am	0 9 * * 1	Weekly on Monday
Weekdays at 9am	0 9 * * 1-5	Mon-Fri at 09:00
Weekends at 10am	0 10 * * 0,6	Sat-Sun at 10:00
First of month	0 0 1 * *	Monthly at midnight
Every quarter	0 0 1 1,4,7,10 *	Jan, Apr, Jul, Oct 1st
Every Sunday at 3am	0 3 * * 0	Weekly maintenance window

Real-World Examples

GitHub Actions

name: Daily Build
on:
  schedule:
    - cron: "0 6 * * *"  # Every day at 6am UTC

Kubernetes CronJob

apiVersion: batch/v1
kind: CronJob
metadata:
  name: backup
spec:
  schedule: "0 2 * * *"  # Every day at 2am
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: backup
            image: backup-tool:latest

Node.js (node-cron)

const cron = require("node-cron");

// Every 5 minutes
cron.schedule("*/5 * * * *", () => {
  console.log("Running health check...");
});

// Every weekday at 9am
cron.schedule("0 9 * * 1-5", () => {
  sendDailyReport();
});

Linux Crontab

# Edit crontab
crontab -e

# Add entries
*/5 * * * * /usr/bin/health-check.sh
0 2 * * * /usr/bin/backup.sh
0 9 * * 1-5 /usr/bin/send-report.sh

# List current crontab
crontab -l

Common Mistakes

1. Forgetting timezone — Cron typically runs in the server's timezone. Always specify or document which timezone your cron uses.

2. Overlapping executions — If a job takes 10 minutes but runs every 5 minutes, you'll have overlapping instances. Use a lock mechanism.

3. Day of month + day of week — When both are set, most cron implementations run on EITHER matching day (OR logic, not AND).

4. Month/day starting at 1 — Minutes and hours start at 0, but months and days start at 1.

Build and validate your cron expressions with our Cron Expression Generator — it shows human-readable descriptions and next execution times.

Related Tools

• Cron Expression Generator — Build cron expressions visually
• Unix Timestamp Converter — Convert timestamps for scheduling
• JSON Formatter — Format configuration files
• Chmod Calculator — Set permissions on cron scripts