How is the timezone applied?

Cron expressions are zone-agnostic by themselves; the next-run calculator interprets fields like "hour=9" in the timezone you select, including DST transitions in that zone.

What happens during DST spring-forward for a 02:30 job?

If 02:30 is skipped that day, the job is typically deferred to the next valid minute (03:00 on standard cron). Some schedulers run it at 03:30 instead — the preview shows what standard cron does.

Why don't my fire times match my server's cron?

Most often a timezone mismatch (server in UTC, you're previewing in local time) or a flavor mismatch (5-field vs 6-field). Set the preview timezone to match your server.

Does the expression leave my browser?

No. The next-run calculation runs locally; nothing is logged.

next N runs · ISO · DST-aware · live

List the next N fire times for a cron

Paste any cron expression and see when it will fire next. Useful for sanity-checking schedules before deploying to crontab, k8s or pg_cron.

Quick Start

How next-runs are computed

The expression is parsed into five fields and walked minute-by-minute until N matches are found. Output uses your browser's timezone.

01
Paste expression
Standard 5-field cron. * = any, */N = step, A-B = range.
Parsing accepts ISO 8601, RFC 3339, RFC 2822, and Unix epoch seconds/milliseconds. The Date constructor handles the rest with browser-engine consistency.
inputISO 8601RFC 3339epochlive
in · timestampcron · ISO
```
*/30 9-17 * * 1-5
```
loaded · ISO 8601zone · ready
02
Pick count
Anywhere from 1 to 100 future fires.
All math runs in UTC internally to avoid DST landmines; presentation converts back to the user’s zone via Intl.DateTimeFormat.
countUTC mathIntlDST-safelive
N · options20 · live
```
count = 20
```
options applied · UTCDST-safe
03
Walk forward
Each candidate minute is tested against the expression.
Output respects the chosen timezone offset (Z vs +05:30) and pads digits per ISO conventions so sorts stay chronological.
walkoffsetzone-awaresortablepadded
step · computedmin · ready
```
tick → match?
```
computed · instantsortable
04
Copy ISO
One click copies all runs as ISO 8601 strings for code or docs.
Copy writes via the Async Clipboard API; nothing pings a time server — the browser’s clock is the only oracle.
copyclipboardno oracledeterministicclient-side
✓ · copiedready · done
```
✓ Copied
```
shipped · ready to shipsuccess

Pro tips

Time math without DST landmines

Always store UTC

Convert to local for display only. UTC storage avoids DST jumps and timezone drift in databases.

Watch leap seconds

POSIX time doesn’t count leap seconds; some systems do. Don’t use timestamps for sub-second precision across boundaries.

Prefer Temporal eventually

The Date API has many quirks. Temporal is shipping in modern engines and handles zones correctly.

Cron is timezone-tricky

Cron expressions run in the daemon’s local zone unless told otherwise. Pin a TZ explicitly for predictable runs.

ISO 8601 sorts naturally

YYYY-MM-DDTHH:mm:ss sorts correctly as a string. Don’t use US-style MM/DD/YYYY for anything machine-readable.

Beware Y2K38

Signed 32-bit Unix timestamps overflow in 2038. Use 64-bit storage end-to-end for long-lived systems.

Use Cases

When to preview cron

Deploys, audits, on-call.

Pre-deploy sanity

Eyeball the schedule before touching crontab. Math runs in UTC under the hood to dodge DST jumps — local time is only for display. That means scheduling logic and date diffs survive March / November fall-back without the classic off-by-one-hour bug.

DST-safe

K8s CronJobs

Verify your schedule string matches the desired window. Browser clock is the only source — no external time server, no privacy leak, no rate limit. Pair with NTP-synced server time for high-accuracy use cases, but for human-scale work the browser clock is plenty.

k8s

GitHub Actions

Confirm UTC firing times for scheduled workflows. ISO 8601 output sorts naturally as strings, perfect for filenames (report-2026-01-15.pdf) and log lines that need chronological ordering without parsing. Drop into S3 keys for free time-bucketing.

ISO-sortable

Database jobs

pg_cron / dbms_scheduler — check before scheduling. Pairs cleanly with cron, scheduled tasks, and timestamped log analysis. The tool's output drops directly into APScheduler, Linux cron, or GitHub Actions schedule expressions without re-formatting.

spec-grade

Outage post-mortem

Was the cron supposed to fire when it didn't? Output respects the chosen timezone offset (Z vs +05:30) so REST APIs and database TIMESTAMP WITH TIME ZONE columns round-trip cleanly. No ambiguity between "noon UTC" and "noon local".

zone-aware

Docs

Paste a list of upcoming fires into a runbook. Confirms the difference between epoch seconds (10 digits) and milliseconds (13 digits) before you commit code that mis-multiplies by 1000 — a classic bug in cross-language time handling.

epoch-accurate

FAQ

Frequently asked questions

Which cron flavour?

Classic 5-field Unix cron. Seconds and year fields aren't supported — use Quartz Converter for those.

What about @hourly shortcuts?

Not handled. Expand them manually (@daily = 0 0 * * *).

Is DST respected?

Runs use your browser timezone, so DST will skip or repeat hours like a real scheduler would.

Max count?

100, to keep walks fast in degenerate expressions.

Is anything sent to a server?

No. Walking happens locally in your browser.

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