Developer Tools · 6 min read
Cron Every 15 Minutes: Expressions, Time Zones and Examples
Understand */15 * * * *, compare common five-field cron schedules, and check time zones, missed runs, and overlap before scheduling a job.
The five-field expression is */15 * * * *
In conventional five-field cron syntax, this expression selects minute 0, 15, 30, and 45 of each hour. It does not mean 15 minutes after you save the configuration. If you enable it at 10:07, the next matching clock time is 10:15, not 10:22.
That distinction matters when moving from a timer that measures an elapsed interval to a schedule that matches calendar fields. A cron expression describes allowed clock values; it does not describe the duration of your program.
Read the fields from left to right
| Position | Field | Value in the example |
|---|---|---|
| 1 | Minute | */15 |
| 2 | Hour | * |
| 3 | Day of month | * |
| 4 | Month | * |
| 5 | Day of week | * |
The step in the minute field produces four matches in each hour. The unrestricted hour, month, and day fields allow those minute matches throughout the calendar. Keep the field order beside the expression when editing it: moving the same characters into another field changes the schedule.
Common schedules to compare
| Expression | Meaning | Example matching times |
|---|---|---|
| */15 * * * * | At quarter-hour boundaries | 10:00, 10:15, 10:30, 10:45 |
| 15 * * * * | At minute 15 of every hour | 10:15, 11:15, 12:15 |
| 0 */2 * * * | At minute 0 of every second hour | 00:00, 02:00, 04:00 |
| 0 9 * * 1-5 | At 09:00 on weekdays | Monday through Friday at 09:00 |
| 0 0 * * * | At local schedule midnight | 00:00 each matching day |
Compare the first two rows carefully. */15 is a step across the minute field, while 15 is one chosen minute. Replacing the first field with a single number changes the number of hourly matches from four to one.
These expressions are inputs to the schedule fields. A user crontab line also needs the command to run. System crontab formats may require an additional user field. The builder generates an expression, not a complete deployment configuration.
Check the scheduler's time zone, not just the browser clock
CalQuanta's previews are calculated in the browser's local environment. Your server or hosted scheduler may use another zone. A preview showing 09:00 therefore does not establish when a production server will run a job. Read the deployment platform's scheduling settings and compare an upcoming run against a known date.
The Linux crontab manual describes time-zone configuration and daylight-saving behavior for the implementation it documents. A skipped or repeated local clock time can matter around a clock change. Check your actual scheduler's documentation rather than assuming every platform handles it identically.
A schedule does not prevent overlapping work
Suppose a scheduled task starts at 10:00 and needs 22 minutes. Another quarter-hour boundary arrives at 10:15 while the earlier invocation is still working. The expression alone does not say what should happen next. Depending on the execution system, another process could start, be skipped, or wait.
Before deploying, decide whether overlap is safe and how your application will handle retries and duplicate work. Test the command itself with the intended working directory, environment, and permissions. A correct schedule cannot repair a command that fails outside your interactive shell.
A short validation workflow
- Confirm the destination uses five fields. Do not paste a Quartz-style expression with a seconds field into this builder.
- Enter
*/15 * * * *and inspect several upcoming times. - Compare the intended time zone with the deployment scheduler's configuration.
- Run the command separately and decide how overlapping or repeated invocations should behave.
- After deployment, inspect execution logs. A preview is not evidence that a real job ran.
The CalQuanta cron expression generator supports building, explaining, and previewing schedules. It does not install a job, run a command, or monitor a server.