Cron Expression for the Last Day of the Month

Classic five-field cron has no value for "the last day of the month". In RunLater, put L in the day-of-month field: 0 9 L * * runs at 09:00 on November 30, December 31, January 31 and February 28 (29 in leap years). A Linux crontab does not accept L, so there you run on days 28 to 31 and let a date check skip every day that is not the last.

Expressions that work in RunLater

The day is worked out in the timezone you set on the request, so "23:30 on the last day" means 23:30 in that zone, not on a server clock. More on that in the timezone guide.

In a Linux crontab

Run on the last four possible days and continue only when tomorrow is the 1st:

# GNU date (most Linux)
0 9 28-31 * * [ "$(date -d tomorrow +\%d)" = "01" ] && /usr/local/bin/month-end.sh

# BSD / macOS date
0 9 28-31 * * [ "$(date -v+1d +\%d)" = "01" ] && /usr/local/bin/month-end.sh

The % signs need a backslash: in a crontab line an unescaped % ends the command and starts its standard input, and the job quietly does the wrong thing.

Or do the check in your endpoint

If the job is a URL, the same trick works in code: schedule 0 9 28-31 * * and return early unless tomorrow is the 1st in your timezone.

const tz = 'America/Chicago';
const tomorrow = new Date(Date.now() + 24 * 60 * 60 * 1000);
const day = new Intl.DateTimeFormat('en-US', { timeZone: tz, day: 'numeric' }).format(tomorrow);
if (day !== '1') return Response.json({ skipped: true });
// ... month-end work

With RunLater you can skip this and use L directly. To check it, paste 0 9 L * * into the cron expression explainer for the next run dates in your timezone.

Related schedules

• First day of every month: 0 0 1 * *
• First Monday, second Tuesday or last Friday of the month
• The full cron expression guide

Frequently asked questions