Cron every month — `0 0 1 * *` explained

The day-of-month field accepts:

• A literal day (1, 15, 28).
• A list of days (1,15 for 1st and 15th).
• A range (1-7 for the first week).
• A step (1-31/3 for every 3rd day).
• The L modifier for “last day” (extended cron only — see the dedicated guide).

The trickiest case: months without a 31st (Feb, Apr, Jun, Sep, Nov). 0 0 31 * * simply doesn't fire in those months. If you want “the last day” semantics, see the last-day-of-month guide.

Linux crontab

0 0 1 * * /path/to/monthly.sh
# Or with @monthly alias:
@monthly /path/to/monthly.sh

Vercel cron jobs

{
  "crons": [
    { "path": "/api/cron/monthly", "schedule": "0 0 1 * *" }
  ]
}

AWS EventBridge

cron(0 0 1 * ? *)
# Or last day of month:
cron(0 0 L * ? *)

Quartz (Java)

Trigger trigger = newTrigger()
    .withSchedule(cronSchedule("0 0 0 1 * ?"))
    .build();
// Last day of month variant:
cronSchedule("0 0 0 L * ?")

• 0 0 1 * * — first of every month at midnight.
• 0 9 1 * * — first of every month at 09:00.
• 0 0 15 * * — fifteenth of every month.
• 0 0 1,15 * * — twice a month (1st and 15th).
• 0 0 L * * — last day of every month (extended cron only).
• 0 0 1 1,4,7,10 * — quarterly (1st of Jan, Apr, Jul, Oct).
• 0 0 1 1 * — yearly (Jan 1st).
• 0 0 * * 0 — every week (~4x as frequent).

• Day 31 doesn't exist everywhere — 0 0 31 * * fires in 7 of 12 months, silently skipping Feb / Apr / Jun / Sep / Nov. If you want the actual last day, use L (extended cron) or the multi-cron pattern.
• February 29 — only fires in leap years. The schedule looks valid but is sparse. Verify on the calendar.
• Long-running monthly jobs — the next firing is 28-31 days away, so “eventual” failures aren't self-healing. Add explicit alerting and a manual rerun procedure.
• Timezone — “monthly at midnight” is very different in UTC vs your local zone. Pin the timezone explicitly for monthly jobs that produce business-facing outputs.