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Cron schedule

Cron every 12 hours

The cron expression for every 12 hours is 0 */12 * * *. It runs twice a day, at 00:00 and 12:00, and is identical to 0 0,12 * * *.

Every 12 hours
Expression0 */12 * * *
Runs2 times a day
systemd OnCalendar*-*-* 0/12:00:00

How it works

*/12 over the hour range 0-23 yields exactly two values, 0 and 12. With the minute fixed at 0 that’s midnight and noon. Many people find the list form 0 0,12 * * * clearer because it names the two hours outright.

The step can’t be anchored to anything but midnight, so if you need 12-hour spacing at other times, write the two hours yourself: 0 6,18 * * * or 30 8,20 * * *. Any pair of hours 12 apart keeps the gap even.

For jobs that must run twice a day in local time, remember the hosted schedulers are UTC. 00:00 and 12:00 UTC are 21:00 and 09:00 in São Paulo, and 19:00/07:00 or 20:00/08:00 in New York depending on DST.

Field-by-field breakdown
FieldValueMeaning
Minute0minute 0 (on the hour)
Hour*/12every 12 hours: 0, 12
Day of month*every day of the month
Month*every month
Day of week*every day of the week

Next runs

Scheduler clock

As on GitHub Actions without timezone, Vercel, Cloudflare and Kubernetes with timeZone "Etc/UTC".

Next run times, computed in your browser from the current time
RunYour timeUTC
1Calculating… 
2  
3  
4  
5  

Ready-to-paste versions

The same schedule for each scheduler, with what differs on each one.

crontab (Linux, macOS, BSD)

crontab -e
# m h dom mon dow  command
0 */12 * * * /usr/local/bin/job.sh >> /var/log/job.log 2>&1
  • cron uses the server’s time zone. On cronie (Fedora, RHEL), a CRON_TZ=Europe/London line above the entry changes the zone for the entries below it.

GitHub Actions

.github/workflows/scheduled.yml
on:
  schedule:
    - cron: '0 */12 * * *'
  workflow_dispatch: {}
  • Runs in UTC unless you set timezone, and only on the default branch. GitHub’s docs warn that scheduled runs can be delayed at busy times and that schedules in public repositories are disabled after 60 days without activity.
  • The start of every hour is GitHub’s busiest slot. If the exact minute doesn’t matter, move the 0 to something like 17 to get picked up sooner.

Kubernetes CronJob

cronjob.yaml
apiVersion: batch/v1
kind: CronJob
metadata:
  name: scheduled-job
spec:
  schedule: "0 */12 * * *"
  timeZone: "Etc/UTC"
  concurrencyPolicy: Forbid
  jobTemplate:
    spec:
      template:
        spec:
          restartPolicy: OnFailure
          containers:
            - name: job
              image: busybox:1.36
              command: ["/bin/sh", "-c", "date; echo running"]
  • spec.timeZone is stable since Kubernetes 1.27; without it, the kube-controller-manager’s zone applies. concurrencyPolicy: Forbid skips a run while the previous Job is still active.

Vercel Cron Jobs

vercel.json
{
  "crons": [
    { "path": "/api/cron", "schedule": "0 */12 * * *" }
  ]
}
  • Vercel always uses UTC, doesn’t accept names like MON or JAN, and won’t let you set both day of month and day of week.
  • This runs more than once a day, so it needs a Pro or Enterprise plan. Per Vercel’s docs, a Hobby deployment with an expression like this fails.

Cloudflare Workers

wrangler.toml
[triggers]
crons = ["0 */12 * * *"]
  • Cron Triggers run on UTC. Changes can take up to 15 minutes to propagate across Cloudflare’s network.

node-cron (Node.js)

scheduler.js
import cron from 'node-cron';

// 6 fields: the first one (seconds) is optional
cron.schedule('0 0 */12 * * *', async () => {
  await runJob();
}, { timezone: 'UTC', noOverlap: true });
  • The schedule lives inside the Node process: if it’s down, nothing runs, and three replicas run the job three times. noOverlap skips a tick while the previous run is still going.

systemd timer

job.timer + job.service
# /etc/systemd/system/job.timer
[Unit]
Description=Run job.service every 12 hours

[Timer]
OnCalendar=*-*-* 0/12:00:00

[Install]
WantedBy=timers.target

# /etc/systemd/system/job.service
[Service]
Type=oneshot
ExecStart=/usr/local/bin/job.sh

# systemctl daemon-reload && systemctl enable --now job.timer
  • Check it with systemd-analyze calendar '*-*-* 0/12:00:00', which prints the normalized form and the next elapse. AccuracySec defaults to 1min, so the start can drift by up to a minute.

Spring @Scheduled and Quartz

Java
@Scheduled(cron = "0 0 */12 * * *", zone = "UTC")
public void runJob() {
    // ...
}

// Quartz CronTrigger:
CronScheduleBuilder.cronSchedule("0 0 0/12 * * ?")
  • In Spring, the first of the 6 fields is seconds; the rest follow standard cron (0 or 7 = Sunday).
  • In Quartz, one of the two day fields must be ?, so the day-of-week field gets it.

Pitfalls

0 12 * * * is once a day

A plain 12 in the hour field is noon only. The every-12-hours schedule needs the step */12 or the list 0,12.

0 */13 * * * is not every 13 hours

It matches hours 0 and 13, so the gaps alternate between 13 and 11 hours. Intervals that don’t divide 24 need an epoch check in the command, as in the crontab(5) notes: run hourly and test $(( $(date +\%s) / 3600 \% 13 )).

A missed run waits 12 hours

If the machine is off at 00:00, cron doesn’t catch up; the next run is at noon. systemd’s Persistent=true or anacron runs the missed job at boot.

Frequently asked questions

What is the cron expression for every 12 hours?
0 */12 * * *, which runs at 00:00 and 12:00. 0 0,12 * * * is the same schedule.
How do I run every 12 hours at 6 AM and 6 PM?
List the hours: 0 6,18 * * *.
Is every 12 hours the same as twice a day?
Every 12 hours is one specific case of twice a day: the two runs are exactly 12 hours apart. 0 9,17 * * * is also twice a day, but with uneven gaps.
What is every 12 hours in Kubernetes?
spec.schedule: "0 */12 * * *", ideally with spec.timeZone set so the two runs land at the local times you expect.

Last reviewed by Arielton Oberek.