Mastering Cron Expressions for Kubernetes CronJobs

You want your backup job to run “every Tuesday at 3 AM.” You write: * 3 * * 2. Or is it 0 3 * * 2?

Cron expressions are notoriously hard to memorize. In Kubernetes, a bad expression means your job never runs—or runs every minute and bankrupts you.

The 5 Fields of Standard Cron

┌───────────── minute (0 - 59)
│ ┌───────────── hour (0 - 23)
│ │ ┌───────────── day of the month (1 - 31)
│ │ │ ┌───────────── month (1 - 12)
│ │ │ │ ┌───────────── day of the week (0 - 6)
* * * * *

Common Mistakes:

1. Using * for “Once”: * 14 * * * means “Every minute of the 14th hour” (14:00, 14:01… 14:59). You meant 0 14 * * *.
2. Timezone Confusion: Kubernetes CronJobs run in UTC by default. 3 AM UTC might be 10 PM EST (the previous day). Always check the .spec.timeZone field (added in K8s 1.27).

Tools to Generate Expressions

Don’t write them by hand. Use a Cron Expression Generator. These tools visualize the schedule:

• “Next run: 2026-01-20 03:00:00”
• “Next run: 2026-01-27 03:00:00”

[!TIP] Need a sanity check? We’re building a simpler Cron tool. For now, check your node costs on our Cluster Cost Calculator to see how expensive those nightly jobs really are.