Cron monthly on the last day at 18:00: the expression, explained, in Docker

The cron expression for “monthly on the last day at 18:00” is 0 18 28 * *. This page shows what each field does, the next five times it will fire, the mistake most people make with it, and a working Docker example you can paste.

The expression

0 18 28 * *
FieldValueMeaning
minute0exactly 0
hour18exactly 18
day of month28exactly 28
month*every month
day of week*every day of week

Next five runs (UTC, from now)

  1. 2026-09-28 18:00 UTC
  2. 2026-10-28 18:00 UTC
  3. 2026-11-28 18:00 UTC
  4. 2026-12-28 18:00 UTC
  5. 2027-01-28 18:00 UTC

Mistakes people make with this schedule

  • Cron has no "last day of the month". Day 28 is the latest date every month has, so it is the portable choice; "L" only works in Quartz-style schedulers, and 31 silently skips short months.
  • Assuming the server clock is your clock. Cron runs in the machine’s timezone unless the runtime says otherwise; the examples here are UTC.
  • No lock around a job that might overlap itself, and no alert when it silently stops. That second one is what Supercrontab is for.

Run it in your stack

Linux crontabLaravelWordPressNext.js / VercelNode.jsPythonDockerGitHub Actions
# Dockerfile
RUN apk add --no-cache curl
RUN echo '0 18 28 * * curl -fsS http://app:3000/cron/run' > /etc/crontabs/root
CMD ["crond", "-f", "-l", "2"]

Or skip the sidecar: expose the route and let Supercrontab call it.

Questions

Does 0 18 28 * * run in my local time?

Only if the scheduler is configured for it. crontab uses the system timezone; Vercel and GitHub Actions always use UTC; Laravel and node-cron take a timezone option. In Supercrontab the timezone is a field on the job.

What if the previous run is still going?

Classic cron starts the next run anyway. Add a lock (flock on Linux, withoutOverlapping() in Laravel) or let Supercrontab skip the tick while the previous request is open.

Is there a shorter way to write this?

No. The five-field form is the shortest portable version.