What's the difference between 'twice daily' and 0 */12 * * *?

They can produce the same result, but */12 defaults to midnight and noon specifically, while 'twice daily' usually implies you pick two meaningful hours explicitly, like 8 AM and 8 PM.

What's a common twice-daily pattern for business reports?

9 AM and 5 PM (0 9,17 * * 1-5) is common for workday start/end summaries, restricted to weekdays with a day-of-week range.

Can I run twice daily with different logic each time?

Not from a single cron entry — if the morning and evening runs need different behavior, either branch on the current hour inside your script, or use two separate crontab entries.

Cron: Twice Daily

"Twice daily" is less about a specific expression and more about intent — running something at two meaningful points in the day, like a morning and evening reminder, report, or sync. Unlike the raw */12 step (which defaults to midnight and noon), a twice-daily schedule is usually written as an explicit list of the two hours that actually matter.

0 8,20 * * *

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Examples & Variations

0 8,20 * * *

8 AM and 8 PM

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0 9,17 * * 1-5

9 AM and 5 PM, weekdays (start/end of workday)

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0 6,18 * * *

6 AM and 6 PM

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Common Mistakes

Reaching for */12 out of habit — it works, but silently defaults to midnight and noon, which is rarely when a human-facing 'twice daily' reminder should actually fire.
Picking two hours without considering timezone — a twice-daily schedule meant for users in a specific region needs its hours computed in that region's local time, not server time.
Assuming 'twice daily' always means evenly 12 hours apart — a workday-bounded pattern (like 9 AM and 5 PM) is a genuinely different, and very common, twice-daily shape.

Best Practices

Write the two hours explicitly (0 8,20 * * *) rather than via a step value — it's immediately readable and doesn't default to an arbitrary midnight/noon split.
For anything reaching real users, pick hours based on when they're actually likely to engage, not just an even 12-hour split.
If the two runs serve different purposes (like a morning summary and an evening wrap-up), consider whether they're really the same job on one schedule, or two separate cron entries with different logic.

Frequently Asked Questions

What's the difference between 'twice daily' and 0 */12 * * *?: They can produce the same result, but */12 defaults to midnight and noon specifically, while 'twice daily' usually implies you pick two meaningful hours explicitly, like 8 AM and 8 PM.
What's a common twice-daily pattern for business reports?: 9 AM and 5 PM (0 9,17 * * 1-5) is common for workday start/end summaries, restricted to weekdays with a day-of-week range.
Can I run twice daily with different logic each time?: Not from a single cron entry — if the morning and evening runs need different behavior, either branch on the current hour inside your script, or use two separate crontab entries.

Related Tools

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Cron: Every 12 Hours

The cron expression for every 12 hours is 0 */12 * * *, firing twice a day at midnight and noon. See examples, mistakes, and best practices.

Cron: Every Weeknight

The cron expression for every weeknight is 0 18 * * 1-5, running weekday evenings only. See examples, mistakes, and best practices.

Cron: Every Other Day

Standard cron can't natively express 'every other day' across month boundaries. See the common day-of-month workaround, its limitations, and alternatives.