Cron Expression Syntax Explained With Examples

What Is a Cron Expression?

A cron expression is a string of five (or six) fields that define a schedule for automated tasks. Cron jobs are used everywhere — from Linux servers running nightly backups to AWS Lambda functions and Node.js schedulers.

The classic five-field format:

* * * * *
│ │ │ │ └─ Day of week (0–7, where 0 and 7 = Sunday)
│ │ │ └─── Month (1–12)
│ │ └───── Day of month (1–31)
│ └─────── Hour (0–23)
└───────── Minute (0–59)

Field-by-Field Breakdown

Each field accepts:

• A number — exact value (e.g. 5)
• An asterisk * — every possible value
• A range a-b — every value from a to b (e.g. 1-5)
• A step /n — every nth value (e.g. */10 = every 10 minutes)
• A list a,b,c — specific values (e.g. 1,15,30)

Common Cron Expression Examples

Expression	Meaning
* * * * *	Every minute
0 * * * *	Every hour, on the hour
0 9 * * *	Every day at 9:00 AM
0 9 * * 1	Every Monday at 9:00 AM
30 18 1 * *	1st of every month at 6:30 PM
*/15 * * * *	Every 15 minutes
0 8-17 * * 1-5	Every hour from 8 AM to 5 PM, weekdays only

Six-Field Cron (with Seconds)

Some systems (AWS CloudWatch, Spring, many Node.js libraries) support a six-field format with a seconds field at the start:

* * * * * *
│ │ │ │ │ └─ Day of week
│ │ │ │ └─── Month
│ │ │ └───── Day of month
│ │ └─────── Hour
│ └───────── Minute
└─────────── Second (0–59)

Special Strings (Linux cron)

@reboot     # Run once at startup
@hourly     # Same as 0 * * * *
@daily      # Same as 0 0 * * *
@weekly     # Same as 0 0 * * 0
@monthly    # Same as 0 0 1 * *

Real-World Use Cases

• Database backups — 0 2 * * * (every day at 2 AM)
• Cache invalidation — */10 * * * * (every 10 minutes)
• Weekly reports — 0 7 * * 1 (Monday morning at 7 AM)
• SSL cert renewal — 0 3 * * * (daily, off-peak)
• Health checks — */5 * * * * (every 5 minutes)

Common Mistakes to Avoid

• Day-of-week numbering: 0 and 7 both mean Sunday on most systems, but not all
• Month is 1-indexed: January = 1, not 0
• Timezone confusion: Cron runs in the system timezone — often UTC on servers

Validate Your Cron Expressions Instantly

Building cron schedules by hand is error-prone. Use the free Cron Expression Parser on konvertio.app to validate your expressions, see the next execution times, and understand what each field means.