How to Write Cron Expressions — A Beginner's Step-by-Step Guide

Cron expressions tell computers when to run tasks automatically. If you have never written one before, the five-field format looks intimidating — but each field answers one simple question, and you can learn the entire syntax in under 10 minutes.

The Five Fields

Every cron expression is five values separated by spaces. Read them left to right:

Position	Field	Range	Question It Answers
1st	Minute	0-59	At which minute?
2nd	Hour	0-23	At which hour? (24-hour clock)
3rd	Day of Month	1-31	On which day of the month?
4th	Month	1-12	In which month?
5th	Day of Week	0-6 (0=Sunday)	On which day of the week?

That is the entire structure. Five questions, five answers. When all five conditions match the current time, your task runs.

Step 1 — Start With a Simple Schedule

Build cron expressions by starting simple and adding specificity:

• Every minute: * * * * * — all five fields are "every value"
• Every day at midnight: 0 0 * * * — minute 0, hour 0, every day
• Every Monday at 9 AM: 0 9 * * 1 — minute 0, hour 9, any date, any month, Monday

Notice the pattern: specific values narrow the schedule, asterisks keep it open.

Step 2 — Learn the Four Special Characters

Character	Meaning	Example	Result
*	Every value	* * * * *	Every minute
/	Step (every Nth)	*/5 * * * *	Every 5 minutes
-	Range	0 9-17 * * *	Every hour from 9 AM to 5 PM
,	List	0 9 * * 1,3,5	9 AM on Mon, Wed, Fri

Step 3 — Build Common Schedules

Walk through these examples to see how the fields work together:

Every 5 minutes:

• */5 * * * * — the /5 creates steps of 5 in the minute field. Runs at :00, :05, :10, :15... every hour, every day.

Every hour at the 30-minute mark:

• 30 * * * * — minute 30, every hour. Runs at 12:30, 1:30, 2:30... every day.

Every weekday at 9 AM:

• 0 9 * * 1-5 — minute 0, hour 9, any date, any month, Monday through Friday.

Twice a day (9 AM and 5 PM):

• 0 9,17 * * * — minute 0, hours 9 and 17 (comma creates a list), every day.

First of every month at midnight:

• 0 0 1 * * — minute 0, hour 0, day 1, every month, any day of week.

Every 15 minutes during business hours on weekdays:

• */15 9-17 * * 1-5 — every 15 minutes, hours 9-17, any date, any month, Mon-Fri. This combines steps, ranges, and day-of-week filtering in one expression.

Step 4 — Use the Generator to Verify

1. Open the Cron Expression Generator
2. Type or build your expression
3. Read the human-readable description — it tells you exactly when the job will run
4. Check the next execution times to confirm the schedule matches your intent
5. Copy and paste into your crontab or scheduler config

This verification step catches the most common mistake: writing an expression that runs far more or less often than you intended.

Common Gotchas for Beginners

Mistake	What You Wrote	What Happens	Correct Expression
Star in minute field	* 9 * * *	Runs every minute from 9:00 to 9:59 (60 times)	0 9 * * *
Wrong day-of-week number	0 9 * * 7	Sunday on some systems, error on others	0 9 * * 0 (Sunday)
Both day fields set	0 9 15 * 1	Runs on the 15th AND every Monday (OR logic)	Use only one day field
Month names misspelled	0 9 1 Janu *	Error — use JAN or 1	0 9 1 1 * or 0 9 1 JAN *
24-hour time confusion	0 9 * * * (expecting PM)	Runs at 9 AM, not 9 PM	0 21 * * * (9 PM = hour 21)
Forgetting leading zero	9 * * * * vs 09	Both work — cron ignores leading zeros	Either format is fine

Day-of-Week Reference

Number	Day	Mnemonic
0	Sunday	Start of week (Unix convention)
1	Monday
2	Tuesday
3	Wednesday
4	Thursday
5	Friday
6	Saturday

Some systems accept 7 for Sunday as well, but 0 is universal. When in doubt, use 0.

Practice Exercises

Try building these schedules yourself, then verify with the generator:

1. Every 10 minutes — */10 * * * *
2. Every day at 3:30 PM — 30 15 * * *
3. Every Tuesday and Thursday at 8 AM — 0 8 * * 2,4
4. Every first and fifteenth of the month at noon — 0 12 1,15 * *
5. Every 6 hours starting at midnight — 0 */6 * * *

Developer Tools for Your Workflow

• Cron Expression Generator — build and validate cron schedules
• Code Explainer — paste code and get plain-English explanations of what it does
• JSON Formatter — format config files containing cron settings
• Timestamp Converter — convert timezones for scheduling across regions
• Code Formatter — clean up shell scripts triggered by cron
• SQL Formatter — format database queries run by scheduled jobs
• Regex Tester — test log patterns for cron job output parsing