Will my cron job skip or run twice on daylight saving?
Cron has no opinion about daylight saving. It asks the system what the local time is, and twice a year the answer is unusual: one morning 02:30 never happens, and one morning it happens twice.
A schedule written as "02:30 every day" is therefore not a promise that it runs every day. Whether that matters depends on the job — a cache warm can miss a morning, a billing run cannot bill twice.
A worked example
The verdict below is produced by running the verifier on this input — the same code the tool runs in your browser, not a description of it written alongside.
Expression
30 2 * * *
Timezone
America/New_York
Evaluated at
2026-03-07T12:00:00.000Z
The tool evaluates from today, so it will show the next eight runs from now rather than the March date pinned above — and no warning, because the next gap is months away. Use “Load an example” in the schedule panel to pin the clock to the date that reproduces it.
What this checks
- Whether the local time named by the expression exists on every day in the chosen zone.
- Which dates repeat an hour, so a schedule inside it fires twice.
- The next eight runs as absolute UTC instants, not just local wall-clock times.
What it does not tell you
- What your scheduler actually does. Cron implementations differ on how they treat a skipped hour, and some run the missed job late instead of dropping it.
- That the job is idempotent. A repeated run is only a problem if running twice is a problem, and only you know that.
Questions
Which times are affected?
Any local time inside the hour that the zone skips or repeats. For most of the United States and Europe that is somewhere between 01:00 and 03:00, and the exact hour differs by zone. Scheduling outside that window avoids the problem entirely.
Does using UTC fix it?
Yes. UTC has no daylight saving, so every local time exists exactly once every day. That is why infrastructure schedules are usually written in UTC even when the people reading them are not.
Is this checked against a real timezone database?
It uses the timezone data built into your browser, through the standard Intl APIs. Nothing is sent anywhere, and no timezone database is downloaded.
Related
Everything runs in your browser — nothing you paste is uploaded. Read more about local processing or this verifier in the docs.