Cron Expression Every 15 Minutes: */15 * * * * Explained

What does */15 * * * * mean?

A cron expression has five fields separated by spaces. From left to right they are: minute, hour, day of month, month, and day of week. Each field controls when the job runs in that time unit.

*/15 * * * *
│    │ │ │ └─ day of week  (0–6, Sun=0)
│    │ │ └─── month        (1–12)
│    │ └───── day of month (1–31)
│    └─────── hour         (0–23)
└──────────── minute       (0–59)  ← */15 means "every 15 minutes"

The */15 syntax means "every 15 units starting from 0." In the minute field, that produces: 0, 15, 30, 45. The four asterisks in the remaining fields mean "every" — so this runs at those minute values during every hour, every day, every month, and every day of the week.

In plain English: run this job 4 times per hour, 96 times per day.

How the */n step syntax works

The forward slash in */n is called a "step value." It tells cron to pick every nth value from the full range. For the minute field (0–59), */15 selects: 0, 15, 30, 45.

You can think of it as: start at 0, keep adding 15, stop when you exceed 59.

Common interval variations

Run every 15 minutes only during business hours

If you want every 15 minutes but only from 9 AM to 5 PM, combine the step value with a range in the hour field:

*/15 9-17 * * *

This runs every 15 minutes, but only between 9:00 and 17:00 (5 PM). Outside those hours, the job is skipped.

Run every 15 minutes on weekdays only

*/15 9-17 * * 1-5

The 1-5 at the end means Monday through Friday (weekdays). Sunday is 0, Saturday is 6.

Common mistake: using seconds

Standard Unix cron does not have a seconds field. If you need sub-minute precision, you need a different scheduler. Tools like AWS EventBridge, Kubernetes CronJob, or Spring Scheduler support seconds — but their syntax differs from standard crontab.

In standard cron, the smallest unit is one minute. If you put 6 fields, most systems will throw an error or silently ignore the extra field.

How to add this to your crontab

1. Open your crontab with crontab -e
2. Add a new line with your expression and command
3. Save and exit — the cron daemon picks it up immediately

# Run a script every 15 minutes
*/15 * * * * /home/user/scripts/check.sh

# Run every 15 min and log output
*/15 * * * * /home/user/scripts/check.sh >> /var/log/check.log 2>&1

Quick summary

• */15 * * * * — every 15 minutes, all day, every day
• */15 9-17 * * * — every 15 min, 9 AM to 5 PM only
• */15 9-17 * * 1-5 — every 15 min during business hours, weekdays only
• The */n syntax works in any cron field, not just minutes
• Standard cron has no seconds field — smallest unit is one minute