Cron expression for every 12 hours

Field breakdown

Next runs

How this schedule works

Cron evaluates the five fields of 0 */12 * * * — minute, hour, day of month, month, day of week — against the clock once a minute and starts the job on any minute where all five match, which cronstrue reads as "On the hour, every 12 hours": 2 runs per day. The runs land at 00:00, 12:00. Twenty-four divides by 12 without a remainder, so the spacing survives midnight: the gap from the 12:00 run to the next day's 00:00 run is the same 12 hours as every other gap.

When to use every 12 hours

Twice-daily runs suit data exports, morning-and-evening digests, and maintenance heavy enough that you want it split across the day rather than concentrated in one nightly window. Two runs is few enough that each failure is worth looking at individually rather than in aggregate. The catch is placement: a step of 12 is locked to 00:00 and 12:00, which on a UTC-based scheduler can put both runs at inconvenient local hours. When the times matter to a human reader, list the hours explicitly instead of stepping.

Common mistakes with every 12 hours

The step locks the runs to 00:00 and 12:00 and there is no way to move them while keeping the step, which is where most twelve-hour schedules go wrong: someone wants 06:00 and 18:00, writes 0 */12 * * * anyway, and the two runs land in the wrong halves of the day. Use the list form when the placement matters. The other failure is treating the pair as interchangeable. A midnight run and a noon run see very different system load and very different volumes of data, and the job that finishes comfortably at 00:00 can time out at 12:00.

Platform snippets

The same expression, ready to paste into the four schedulers that read five-field cron. The notes below each snippet are the ones that follow from this schedule; the cron expression generator lists every caveat for every platform.

name: Scheduled workflow
on:
  schedule:
    - cron: '0 */12 * * *'
  workflow_dispatch:

jobs:
  scheduled:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Run job
        run: echo "Running scheduled job"

apiVersion: batch/v1
kind: CronJob
metadata:
  name: my-cron-job
spec:
  schedule: "0 */12 * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
            - name: job
              image: my-image:latest
              command: ["/bin/sh", "-c", "echo Running"]
          restartPolicy: OnFailure

{
  "$schema": "https://openapi.vercel.sh/vercel.json",
  "crons": [
    {
      "path": "/api/cron",
      "schedule": "0 */12 * * *"
    }
  ]
}

# Edit your crontab: crontab -e
0 */12 * * * /path/to/command

# With logging:
0 */12 * * * /path/to/command >> /var/log/cron.log 2>&1

Variations

• 0 0,12 * * * At 12:00 AM and 12:00 PM The identical pair of hours as a list. Same result, and it can be edited to any two hours without abandoning the form.
• 0 6,18 * * * At 06:00 AM and 06:00 PM The same twelve-hour rhythm moved to 06:00 and 18:00. A step cannot express this; only the list form can move the pair off midnight.
• 0 */6 * * * On the hour, every 6 hours Four runs a day instead of two. The step up when twelve hours of accumulated work is more than one invocation can chew through.
• 0 */12 * * 1-5 On the hour, every 12 hours, Monday through Friday Twice a day on weekdays only, cutting fourteen runs a week to ten. The weekend gap reaches 60 hours, which the job has to survive.