Cron Expression Generator

Upcoming run times for a five-field cron expression, evaluated in UTC from an explicit or current reference instant.

How it works

• Split the expression into the five standard fields.
• Expanded ranges, lists, steps, and month/day names into value sets.
• Scanned forward minute by minute (bounded to one year) for matching UTC instants.

• Cron uses UTC and runs the day-of-month and day-of-week rules with OR semantics when both are restricted.

Methodology

1. Parse the five fields (minute, hour, day-of-month, month, day-of-week) using the POSIX crontab field grammar, including lists, ranges, steps, and names.
2. Evaluate each candidate instant against the fields in UTC; when both day fields are restricted, match if either matches.
3. Stop after one year if no instant matches, rather than looping forever.

Time model

• Time source: UTC.
• Timezone: Cron fields are evaluated in UTC and run times are rendered in UTC with a Z offset. UTC is the default and is stated on the page and in the interactive result.
• Locale: Month and weekday names are the English POSIX three-letter names; no locale-specific names are accepted.
• Daylight saving: UTC has no daylight-saving transitions; daylight-saving shifts in other zones are ignored.
• Reference date: Optional reference instant. When omitted, the current instant is read from the visitor's environment at runtime; runs are still evaluated and reported in UTC.

Usage

1. Enter a five-field cron expression (minute hour day-of-month month day-of-week).
2. Choose how many upcoming runs to list.
3. Read the description and the next run times.

Examples

These are examples, not current values: they use fixed inputs, while the interactive tool computes live results in your browser.

Every 15 minutes on weekday business hours

{
  "expression": "*/15 9-17 * * MON-FRI",
  "count": 3,
  "reference": "2026-01-05T08:00:00.000Z"
}

First of each month at midnight

{
  "expression": "0 0 1 * *",
  "count": 2,
  "reference": "2026-01-15T00:00:00.000Z"
}

Limitations

Reading a cron field

A field is a comma list of items. Each item is a single value, a range (1-5), a step (*/15 or 1-30/5), or a wildcard. Month and day-of-week accept three-letter names.

Why UTC matters

Many schedulers interpret cron in the server's local time. This tool uses UTC explicitly so that the listed run times are unambiguous.