Run Monthly Task on the 15th at 9:30 PM | CronBase
15 21 15 * * Once a month, on the 15th day at 9:30 PM
* In a Nutshell
The cron expression 15 21 15 * * runs Once a month, on the 15th day at 9:30 PM. Running jobs precisely on a specific day of the month, like the 15th, is crucial for financial reporting, billing cycles, or complex monthly maintenance tasks. This cadence ensures timely data aggregation and prevents delays in critical business processes that rely on monthly data cutoffs.
* When to use this
Use 15 21 15 * * when a recurring task needs to run Once a month, on the 15th day at 9:30 PM. This schedule is commonly associated with end of month and monthly schedules and report generation workloads. It uses Standard (5-Field POSIX) syntax, supported by Unix cron daemons, cloud schedulers such as AWS EventBridge, and container orchestration platforms such as Kubernetes CronJob.
CronBase parses 15 21 15 * * using a dialect-aware rules engine that identifies the Standard (5-Field POSIX) format, validates field structure against the Standard (5-Field POSIX) specification, and produces the translation above. Next run times are calculated by forward-scanning from the current UTC clock. Learn how CronBase works.
Platform Implementations
Bash
Prerequisites
Unix/Linux host with a cron daemon running (vixie-cron, cronie, or systemd-cron). The script at /usr/local/bin/run-task.sh must exist and be executable (chmod +x).
Configuration
Run crontab -e to open the crontab editor. Cron reads the server's local timezone; prefix with CRON_TZ=UTC before the expression to pin to UTC. Always redirect output with >> /var/log/cron-tasks.log 2>&1 to capture both stdout and stderr.
Gotchas
Cron jobs inherit a minimal PATH — use full binary paths or set PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin at the top of the crontab. For sub-hourly schedules, add flock -n /tmp/run-task.lock before the command to skip overlapping runs if the previous execution is still running.
# Add to crontab with: crontab -e
15 21 15 * * /usr/local/bin/run-task.sh >> /var/log/cron-tasks.log 2>&1Last verified:
Nodejs
Prerequisites
Node.js 18+ with node-cron installed (npm install node-cron). Add "type": "module" to package.json to use the import syntax shown above.
Configuration
Pass { timezone: 'UTC' } as the third argument to cron.schedule(). Without this option the schedule uses the Node.js process timezone, which shifts during DST transitions when servers are not pinned to UTC.
Gotchas
node-cron uses standard 5-field cron syntax — not Quartz 6-field. If your job runs longer than the schedule interval the next trigger fires while the previous is still executing. Use a boolean guard or a queue to skip concurrent runs rather than relying on the scheduler to enforce it.
import cron from 'node-cron';
cron.schedule('15 21 15 * *', async () => {
console.log('[cron] running at', new Date().toISOString());
// your task logic here
}, { timezone: 'UTC' });Last verified:
Python
Prerequisites
Python 3.8+ with apscheduler installed (pip install apscheduler). For Python 3.12+ use apscheduler>=3.10.
Configuration
CronTrigger.from_crontab() accepts a standard 5-field cron string. Always pass timezone='UTC' to both the BlockingScheduler constructor and the trigger to ensure consistent scheduling regardless of the server's locale.
Gotchas
BlockingScheduler.start() blocks the calling thread indefinitely. For a web application, use BackgroundScheduler instead and call scheduler.start() at application startup. APScheduler logs missed fires if the process is stopped and restarted — configure misfire_grace_time (in seconds) to control how late a missed job is allowed to run.
from apscheduler.schedulers.blocking import BlockingScheduler
from apscheduler.triggers.cron import CronTrigger
scheduler = BlockingScheduler(timezone='UTC')
@scheduler.scheduled_job(
CronTrigger.from_crontab('15 21 15 * *', timezone='UTC')
)
def run_task() -> None:
print('task running')
# your task logic here
scheduler.start()Last verified:
Golang
Prerequisites
Go 1.18+ and github.com/robfig/cron/v3 (go get github.com/robfig/cron/v3).
Configuration
Always create the scheduler with cron.New(cron.WithLocation(time.UTC)). Without WithLocation, the library defaults to the server's local timezone. Call c.Start() to begin the scheduler, then block with select {} to keep the process alive.
Gotchas
robfig/cron v3 uses standard 5-field cron expressions by default. To add second-level precision (6 fields), pass cron.WithSeconds() to cron.New() — but this changes field positions, so never mix syntaxes in the same scheduler. Always check the error returned by c.AddFunc() — a malformed expression is silently ignored without it.
package main
import (
"fmt"
"time"
"github.com/robfig/cron/v3"
)
func main() {
c := cron.New(cron.WithLocation(time.UTC))
_, err := c.AddFunc("15 21 15 * *", func() {
fmt.Println("task running at", time.Now().UTC())
// your task logic here
})
if err != nil {
panic(err)
}
c.Start()
defer c.Stop()
select {}
}Last verified:
Java
Prerequisites
Spring Boot 2.7+ (or Spring Framework 5.3+) with spring-context on the classpath. Annotate your @SpringBootApplication class with @EnableScheduling — without it, @Scheduled methods are silently ignored.
Configuration
Spring @Scheduled uses a 6-field Quartz-style expression: [sec] [min] [hr] [dom] [mon] [dow]. The expression 0 15 21 15 * ? is derived from 15 21 15 * * — a leading 0 is prepended for the seconds field, and ? replaces the unconstrained day field.
Gotchas
Standard Unix cron has 5 fields; Spring requires 6. Pasting a 5-field expression directly into @Scheduled shifts every field by one and the job misfires silently. Use ? for either dom or dow — Quartz does not allow both to be *.
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
@Component
public class ScheduledTask {
@Scheduled(cron = "0 15 21 15 * ?")
public void runTask() {
System.out.println("task running at: " + java.time.Instant.now());
// your task logic here
}
}Last verified:
Kubernetes
Prerequisites
Kubernetes 1.21+ (CronJob API is GA). kubectl configured with cluster access. Container image must be pullable from within the cluster.
Configuration
Apply with kubectl apply -f cronjob.yaml. Check status with kubectl get cronjobs and inspect run history with kubectl get jobs. concurrencyPolicy: Allow is set because this schedule fires infrequently — parallel runs are acceptable.
Gotchas
Without startingDeadlineSeconds, a missed job (e.g., due to cluster downtime) triggers as soon as the controller recovers. Kubernetes 1.25+ supports timeZone: UTC in the spec to avoid timezone ambiguity. Keep successfulJobsHistoryLimit and failedJobsHistoryLimit low to avoid accumulating stale Job objects in the cluster.
apiVersion: batch/v1
kind: CronJob
metadata:
name: scheduled-task
spec:
schedule: "15 21 15 * *"
concurrencyPolicy: Allow
jobTemplate:
spec:
template:
spec:
restartPolicy: OnFailure
containers:
- name: task
image: alpine:3.19
command: ["/bin/sh", "-c", "echo 'task running'"]Last verified:
AWS EventBridge Equivalent
Standard cron expressions often need conversion for AWS EventBridge schedules.
cron(15 21 15 * ? *)Frequently Asked Questions
What does the `15 21 15 * *` cron expression actually do?
This cron expression is set to execute a task specifically on the 15th day of every calendar month, precisely at 9:30 PM. It will trigger once per month on this designated date and time.
How does this schedule handle time zone changes and Daylight Saving Time?
Cron jobs typically run based on the server's local time zone settings. Changes due to Daylight Saving Time will be automatically observed by the scheduler, potentially shifting the exact clock time when the job runs relative to UTC.
How can I verify that my task is running correctly with this schedule?
To confirm the schedule is working, check your task's execution logs. Look for entries that appear consistently on the 15th of each month around 9:30 PM. You can also temporarily add a logging step to your task to explicitly record its start time.
Are there any potential pitfalls with running a job on the 15th of the month?
A key consideration is ensuring your system can handle the workload if the 15th happens to fall on a weekend or holiday, and if subsequent processing depends on this task completing. Plan for potential delays if the 15th requires manual intervention or falls within a period of reduced operational capacity.
What is a common variation for this type of monthly schedule?
A frequent variation is to schedule the task for the first day of the month instead of the fifteenth, which is often used for processing monthly reports or performing system cleanups at the very beginning of a new billing cycle.
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