Cron Next Runs

Parses standard 5-field cron (minute hour day month weekday) with ranges (1-5), lists (1,3,5), steps (*/15), and month / weekday aliases (mon, jan). The result list shows the next runs starting from now (or a fixed timestamp), in your local timezone. When both day-of-month and day-of-week are restricted, either match counts as a hit — matching the original Vixie cron semantics.

That last rule is the one worth reading twice, because it is a union and not an intersection. 0 0 13 * 5 fires on the 13th of every month and on every Friday, which comes to about 62 days a year rather than the 1.7 that are actually a Friday the 13th. The list of upcoming runs is the fastest way to catch this: if a schedule you meant to be rare shows a run tomorrow, the two day fields are fighting. When only one of the two is restricted the rule does not apply, and the schedule reads exactly as you would expect.

Step values are computed over the field's own range rather than as a repeating interval from the last run. */15 in the minute field means minutes 0, 15, 30 and 45, not "every fifteen minutes from whenever the job last ran", and 0 */5 * * * restarts its count at midnight, so the gap between the 20:00 run and the next one is four hours rather than five. Ranges combined with steps, as in 10-40/10, step within the range only.

Times are shown in your browser's timezone, which is a convenience for reading and a trap for deploying. A cron daemon uses the local time of its own host, and most hosted schedulers run in UTC no matter where you are. Around a daylight saving transition the two diverge visibly: a daily job in the skipped hour has no run that day, and one in the repeated hour has two.