AirflowHow-ToBeginner · 4 min read

How to Use Cron Expression in Airflow for Scheduling

In Airflow, you use a cron expression in the schedule_interval parameter of a DAG to define when it runs. This expression follows standard cron syntax like "0 12 * * *" to run daily at noon.

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Syntax

A cron expression in Airflow uses five fields separated by spaces: minute, hour, day of month, month, and day of week. Each field controls when the DAG runs.

Minute: 0-59
Hour: 0-23
Day of Month: 1-31
Month: 1-12
Day of Week: 0-6 (Sunday=0)

Example: "0 12 * * *" means run at 12:00 PM every day.

python

schedule_interval = "0 12 * * *"

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Example

This example shows how to create a simple Airflow DAG that runs every day at 7:30 AM using a cron expression in schedule_interval.

python

from airflow import DAG
from airflow.operators.bash import BashOperator
from datetime import datetime

with DAG(
    dag_id='daily_7_30_am',
    start_date=datetime(2024, 1, 1),
    schedule_interval='30 7 * * *',  # Runs daily at 7:30 AM
    catchup=False
) as dag:
    task = BashOperator(
        task_id='print_date',
        bash_command='date'
    )

Output

When the DAG runs at 7:30 AM, the task prints the current date and time in the Airflow logs.

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Common Pitfalls

Common mistakes when using cron expressions in Airflow include:

Using the wrong number of fields (Airflow expects 5 fields, not 6 like some cron versions).
Confusing day of week and day of month fields, which can cause unexpected schedules.
Forgetting that Airflow uses UTC time by default, so scheduled times may differ from your local time.
Using schedule_interval='@daily' if you want a simple daily run instead of a cron expression.

Always test your cron expression with an online cron tester to verify the schedule.

python

## Wrong: 6 fields (unsupported in Airflow)
schedule_interval = "0 12 * * * *"

## Right: 5 fields
schedule_interval = "0 12 * * *"

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Quick Reference

Field	Allowed Values	Description	Example
Minute	0-59	Minute of the hour	30
Hour	0-23	Hour of the day (24h)	7
Day of Month	1-31	Day of the month	*
Month	1-12	Month of the year	*
Day of Week	0-6	Day of the week (Sunday=0)	*

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Key Takeaways

Use a 5-field cron expression in the DAG's schedule_interval to set run times.

Airflow cron expressions follow standard syntax: minute, hour, day, month, day of week.

Airflow schedules use UTC time by default; adjust if needed for your timezone.

Test cron expressions with online tools to avoid scheduling errors.

For simple schedules, Airflow supports presets like '@daily' as alternatives.