Cron Expression Generator

A cron expression is a string of characters that defines a recurring schedule for automated tasks. It originates from the Unix cron utility and tells a system exactly when to execute a command or script. A standard expression has five fields — minute, hour, day of month, month, and day of week — separated by spaces. For example, 30 8 * * 1-5 means "at 8:30 AM, Monday through Friday."

Reading left to right, the five fields are: minute (0–59), hour (0–23), day of month (1–31), month (1–12 or JAN–DEC), and day of week (0–6 or SUN–SAT). Each field can contain a specific number, a wildcard * meaning "every", a range like 1-5, a list like 1,15,30, or an increment like */15.

Standard Unix cron has five fields and a minimum precision of one minute. Quartz cron, used primarily in Java and Spring applications, adds a seconds field at the start (giving six fields total) and an optional year field at the end. Quartz also supports additional special characters such as L (last day of the month or week), W (nearest weekday), and # (the nth occurrence of a weekday in a month). Use standard cron for most Unix/Linux system tasks and Quartz when your scheduler or framework specifically requires it.

The asterisk * is the wildcard character meaning "every possible value" for that field. For example, * * * * * runs every minute of every hour of every day. In the hours field, * means every hour; in the month field, it means every month, and so on. It is the most commonly used character in cron expressions.

Use the increment character / in the minutes field: */15 * * * *. This means "every 15 minutes, every hour, every day." The */15 notation is shorthand for "starting at 0, every 15 steps" — so the job runs at :00, :15, :30, and :45 past each hour. To restrict it to business hours only you could write */15 9-17 * * 1-5, which runs every 15 minutes between 9 AM and 5 PM on weekdays.

Specify a fixed minute and hour and use wildcards for the remaining fields. For example, 0 2 * * * runs at exactly 2:00 AM every day. To run at midnight use 0 0 * * *. To run at noon use 0 12 * * *. Choosing an off-peak time like 2–4 AM is common practice for maintenance tasks to minimise impact on users.

Set the day-of-month field to 1: 0 0 1 * * runs at midnight on the first day of every month. To run on the first day of specific months — say January, April, July, and October — you can use a list in the month field: 0 0 1 1,4,7,10 *.

The ? character is used in Quartz cron expressions to mean "no specific value" and is only valid in the day-of-month and day-of-week fields. Because specifying both a day of month and a day of week simultaneously would be contradictory, Quartz requires you to set one of them to ? to avoid conflicts. For example, 0 0 12 15 * ? means "at noon on the 15th of every month, regardless of what day of the week it falls on."

Set the day-of-week field to 1-5, which represents Monday through Friday. For example, 0 9 * * 1-5 runs at 9:00 AM on every weekday. Note that day-of-week numbering varies slightly by system — most Unix systems use 0 or 7 for Sunday, while Quartz uses 1 for Sunday and 7 for Saturday. Using the three-letter abbreviations (MON-FRI) avoids this ambiguity entirely.

The most common causes are timezone mismatches, field numbering confusion, and conflicts between the day-of-month and day-of-week fields. Cron daemons typically run in the server's local timezone — if your server is set to UTC but you are thinking in your local time, the job will appear to run at the wrong hour. The day-of-month and day-of-week fields use OR logic in standard cron: if either condition matches, the job runs, which can lead to more frequent execution than expected. Using an expression validator with a plain-English translation and an execution preview — showing the actual next five run times — is the most reliable way to confirm your expression is correct before deploying it.

Cron runs jobs in the time zone of the server, which is often UTC. The next-run list on this page shows times in your own time zone by default; switch it to UTC to see them the way a UTC server will run them. Some cron versions let you set a time zone with a CRON_TZ= line in the crontab, and Quartz and Spring let you pass a time zone with the schedule.

0 * * * * runs at the start of every hour (i.e., at :00 minutes past each hour). If you want to run at a specific minute past every hour — say 30 minutes past — use 30 * * * *. To run multiple times per hour at fixed intervals, use the increment syntax: */30 * * * * runs every 30 minutes.

Not with standard Unix cron, which has a minimum resolution of one minute. Quartz cron supports a seconds field, so * * * * * ? in Quartz would run every second. However, for sub-minute scheduling on most systems you are better served by a purpose-built task queue or a background worker process rather than a cron-based scheduler, as cron was designed for longer-interval recurring tasks.