Cron expression for twice a day

Field breakdown

Next runs

How this schedule works

Cron evaluates the five fields of 0 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 "At 12:00 AM and 12:00 PM": 2 runs per day. The runs land at 00:00, 12:00, because a comma-separated list matches each value it names and nothing between them.

When to use twice a day

Two runs a day cover the large middle ground between hourly polling and a single nightly batch: a morning and an evening sync, a twelve-hour backup rotation, digests at the start and the middle of the day. Writing the hours as a list rather than a step is the whole point — it lets the two runs sit wherever they are actually useful, twelve hours apart or not, and it states the times plainly for whoever reads the crontab after you. Reach for it whenever one daily run leaves too large a gap.

Common mistakes with twice a day

Two runs a day invite an assumption that rarely holds: that they are equivalent. The midnight run usually processes a full, quiet, closed period; the noon run processes half a day against live traffic. Sizing and timeouts derived from one will not necessarily hold for the other. The expression-level mistake is a stray space — 0 0, 12 * * * is not a valid five-field expression, and cron's error reporting for it is famously unhelpful. Keep lists tight, with no spaces around the commas. And note that Vercel Cron rejects this schedule outright on the Hobby plan, which allows one run per day.

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 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 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 0,12 * * *"
    }
  ]
}

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

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

Variations

• 0 */12 * * * On the hour, every 12 hours The identical schedule written as a step. Shorter, but locked to 00:00 and 12:00 — it cannot express any other pair.
• 0 6,18 * * * At 06:00 AM and 06:00 PM The same twelve-hour spacing shifted six hours, which puts both runs at a civilised local hour in more of the world than midnight and noon do.
• 0 9,17 * * 1-5 At 09:00 AM and 05:00 PM, Monday through Friday Bookends the workday, weekdays only. The two runs are eight hours apart, not twelve, which no step value can express.
• 0 0,8,16 * * * At 12:00 AM, 08:00 AM and 04:00 PM Three runs a day at eight-hour spacing. The step up when twelve hours between runs leaves too much work to do in one.