Cron every 12 minutes: the expression, explained, in Docker

The cron expression for “every 12 minutes” is */12 * * * *. 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

*/12 * * * *

Field	Value	Meaning
minute	*/12	every 12 minutes, starting at 0
hour	*	every hour
day of month	*	every day of month
month	*	every month
day of week	*	every day of week

Next five runs (UTC, from now)

2026-09-17 23:48 UTC
2026-09-18 00:00 UTC
2026-09-18 00:12 UTC
2026-09-18 00:24 UTC
2026-09-18 00:36 UTC

Mistakes people make with this schedule

"*/12" means minutes 0, 12, 24… of the hour, not "12 minutes after the last run". The count restarts at the top of every hour, so a run at :13 is impossible with this expression.
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 crontab Laravel WordPress Next.js / Vercel Node.js Python Docker GitHub Actions

# Dockerfile
RUN apk add --no-cache curl
RUN echo '*/12 * * * * 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 */12 * * * * 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.