Schedule flow runs

Prefect allows you to specify schedules on which your flows run. You can add one or more schedules to any served or deployed flow. Schedules tell Prefect when and how to create new flow runs. You can add a schedule to a deployed flow in the Prefect UI, in the CLI through the prefect deployment schedule command, or the prefect.yaml configuration file.

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Create schedules

There are several ways to create a schedule for a deployment:

• Through the Prefect UI
• With the cron, interval, or rrule parameters if building your deployment with the serve method of the Flow object or the serve utility for managing multiple flows simultaneously
• If using worker-based deployments
  • When you define a deployment with flow.serve or flow.deploy
  • Through the interactive prefect deploy command
  • With the deployments -> schedules section of the prefect.yaml file

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Create schedules in the UI

You can add schedules in the Schedules section of a Deployment page in the UI. To add a schedule select the + Schedule button. Choose Interval or Cron to create a schedule.

The new schedule appears on the Deployment page where you created it. New scheduled flow runs are visible in the Upcoming tab of the Deployment page.

To edit an existing schedule, select Edit from the three-dot menu next to a schedule on a Deployment page.

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Create schedules in Python

Specify the schedule when you create a deployment in a Python file with flow.serve(), serve, flow.deploy(), or deploy. Just add the keyword argument cron, interval, or rrule.

The serve method below will create a deployment of my_flow with a cron schedule that creates runs every minute of every day:

from prefect import flow

from myproject.flows import my_flow

my_flow.serve(name="flowing", cron="* * * * *")

If using work pool-based deployments, the deploy method has the same schedule-based parameters.

When my_flow is served with this interval schedule, it will run every 10 minutes beginning at midnight on January, 1, 2026 in the America/Chicago timezone:

from datetime import timedelta, datetime
from prefect.client.schemas.schedules import IntervalSchedule

from myproject.flows import my_flow

my_flow.serve(
  name="flowing",
  schedules=[
    IntervalSchedule(
      interval=timedelta(minutes=10),
      anchor_date=datetime(2026, 1, 1, 0, 0),
      timezone="America/Chicago"
    )
  ]
)

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Create schedules in the terminal

You can create a schedule through the interactive prefect deploy command. You will be prompted to choose which type of schedule to create.

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Create schedules in YAML

If you save the prefect.yaml file from the prefect deploy command, you will see it has a schedules section for your deployment. Alternatively, you can create a prefect.yaml file from a recipe or from scratch and add a schedules section to it.

deployments:
  ...
  schedules:
    - cron: "0 0 * * *"
      timezone: "America/Chicago"
      active: false
    - cron: "0 12 * * *"
      timezone: "America/New_York"
      active: true
    - cron: "0 18 * * *"
      timezone: "Europe/London"
      active: true

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Schedule types

Prefect supports three types of schedules:

• Cron is most appropriate for users who are already familiar with cron from previous use.
• Interval is best suited for deployments that run at some consistent cadence that isn’t related to absolute time.
• RRule is best suited for deployments that rely on calendar logic for simple recurring schedules, irregular intervals, exclusions, or day-of-month adjustments.

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Cron

You can specify a schedule with a cron pattern. You may also provide a timezone to enforce daylight saving time (DST) behaviors.

Prefect uses croniter to specify datetime iteration with a cron-like format.

Cron properties include:

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How the day_or property works

The day_or property defaults to True, matching the behavior of cron.

In this mode, if you specify a day (of the month) entry and a day_of_week entry, the schedule runs a flow on both the specified day of the month and on the specified day of the week.

The “or” in day_or refers to the two entries treated like an OR statement. The schedule should include both, as in the SQL statement:

SELECT * FROM employees WHERE first_name = 'Ford' OR last_name = 'Prefect';

For example, with day_or set to True, the cron schedule * * 3 1 2 runs a flow every minute on the third day of the month and on Tuesday (the second day of the week) in January (the first month of the year).

With day_or set to False, the day (of the month) and day_of_week entries are joined with the more restrictive AND operation, as in the SQL statement:

SELECT * from employees WHERE first_name = 'Zaphod' AND last_name = 'Beeblebrox';

For example, the same schedule, when day_or is False, runs a flow on every minute on the third Tuesday in January. This behavior matches fcron instead of cron.

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Interval

An Interval schedule creates new flow runs on a regular interval measured in seconds. Intervals are computed using an optional anchor_date.

schedule:
  interval: 600
  timezone: America/Chicago

Interval properties include:

The anchor_date does not indicate a “start time” for the schedule, but a fixed point to compute intervals. If the anchor date is in the future, then schedule dates are computed by subtracting the interval from it. In this example, you import the Pendulum Python package for easy datetime manipulation. Pendulum isn’t required, but it’s a useful tool for specifying dates.

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RRule

An RRule scheduling supports iCal recurrence rules (RRules), which provide convenient syntax for creating repetitive schedules. Schedules can repeat on a frequency from yearly down to every minute.

RRule uses the dateutil rrule module to specify iCal recurrence rules.

RRules are appropriate for any kind of calendar-date manipulation, including simple repetition, irregular intervals, exclusions, week day or day-of-month adjustments, and more. RRules can represent complex logic like:

• The last weekday of each month
• The fourth Thursday of November
• Every other day of the week

RRule properties include:

You may find it useful to use an RRule string generator such as the iCalendar.org RRule Tool to help create valid RRules.

schedule:
  rrule: 'FREQ=WEEKLY;BYDAY=MO,WE,FR;UNTIL=20240730T040000Z'

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How scheduling works

Prefect’s Scheduler service evaluates each deployment’s schedules and creates new runs appropriately. It starts automatically when prefect server start is run and it is a built-in service of Prefect Cloud.

The Scheduler creates the fewest runs that satisfy the following constraints, in order:

• No more than 100 runs will be scheduled.
• Runs will not be scheduled more than 100 days in the future.
• At least three runs will be scheduled.
• Runs will be scheduled until at least one hour in the future.

These behaviors are adjustable through the relevant settings with the prefect config view --show-defaults command:

PREFECT_API_SERVICES_SCHEDULER_DEPLOYMENT_BATCH_SIZE='100'
PREFECT_API_SERVICES_SCHEDULER_ENABLED='True'
PREFECT_API_SERVICES_SCHEDULER_INSERT_BATCH_SIZE='500'
PREFECT_API_SERVICES_SCHEDULER_LOOP_SECONDS='60.0'
PREFECT_API_SERVICES_SCHEDULER_MIN_RUNS='3'
PREFECT_API_SERVICES_SCHEDULER_MAX_RUNS='100'
PREFECT_API_SERVICES_SCHEDULER_MIN_SCHEDULED_TIME='1:00:00'
PREFECT_API_SERVICES_SCHEDULER_MAX_SCHEDULED_TIME='100 days, 0:00:00'

See the Settings docs for more information on altering your settings.

These settings mean that if a deployment has an hourly schedule, the default settings will create runs for the next four days (or 100 hours). If it has a weekly schedule, the default settings will maintain the next 14 runs (up to 100 days in the future).

If you change a schedule, previously scheduled flow runs that have not started are removed, and new scheduled flow runs are created to reflect the new schedule.

To remove all scheduled runs for a flow deployment, you can remove the schedule.