Use a rate expression when a task should repeat at a regular interval; use cron when it must follow a calendar pattern or run at a chosen time. For new scheduled tasks, configure an Amazon EventBridge Scheduler schedule rather than a legacy scheduled rule. Set a time zone explicitly when the schedule follows local time, and treat the scheduled time as a delivery window—not an exact-second guarantee.
Choose by the timing requirement
| Requirement | Best starting point | Reason |
|---|---|---|
| Repeat every fixed interval, such as every five minutes | Rate | It directly expresses a repeating interval. |
| Run at a chosen time or on selected calendar days | Cron | It provides calendar fields and time-of-day control. |
| Follow a local clock across daylight-saving changes | Cron with an explicit time zone | The selected time zone determines how local time and daylight-saving changes are interpreted. |
| Allow invocations to be spread across a permitted period | Either expression with a flexible time window | The window lets Scheduler invoke within the configured interval. |
These are selection guidelines, not performance comparisons: AWS’s documentation does not publish a statistic showing that cron or rate is faster.
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When to use a rate expression
Choose a rate when elapsed intervals matter more than a particular time on the calendar—for example, a recurring job every five minutes or once per day. AWS describes rate-based schedules as useful for regular intervals such as every 15 minutes or every five days (CreateSchedule API reference).
The syntax is rate(value unit). The value must be a positive integer, and the supported units are minutes, hours, and days. Use a singular unit for a value of one and a plural unit for values above one:
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rate(5 minutes)— repeat every five minutes.rate(1 day)— repeat at a daily interval.rate(1 hour)— repeat at an hourly interval.rate(5 hours)— repeat every five hours.
A daily rate describes a repeating interval; it does not specify “9 a.m. local time.” Use cron and a time zone for that kind of wall-clock requirement.
When to use a cron expression
Choose cron when the schedule depends on calendar fields: for example, a particular hour, weekday, or date. EventBridge Scheduler cron expressions have six fields, in this order: minutes hours day_of_month month day_of_week year. Use the fields to define the intended calendar pattern, rather than trying to approximate it with a rate interval. The CreateSchedule API reference documents the expression forms and field order.
If the requirement says “at 9 a.m. in this region,” make the time zone part of the schedule configuration. A cron pattern alone does not say whether its clock should be UTC or local time.
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Set the time zone deliberately
EventBridge Scheduler has a time-zone field that controls how it evaluates a schedule expression. For a job that should follow local civil time, select the intended time zone rather than assuming UTC will remain aligned with local clocks. UTC-based scheduling stays tied to UTC, so its displayed local time can shift when a region changes between standard time and daylight time. AWS explains schedule configuration in its Scheduler user guide and discusses daylight-saving behavior in its troubleshooting guidance.
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Before deployment, verify the intended time zone and consider what the job should do when daylight-saving transitions affect the local clock. The requirement is often best stated in operational terms: “run at 9 a.m. America/New_York time,” rather than simply “run at 9 a.m.”
Understand invocation timing and flexible windows
Neither expression guarantees that a target runs at the exact second indicated by a schedule. AWS troubleshooting guidance says invocations are not clamped to the zero second of a minute; an invocation may occur within the specified minute (Troubleshooting Amazon EventBridge Scheduler).
A flexible time window gives Scheduler permission to invoke within a configured period after the scheduled time. That can spread invocation load when a task does not need a narrow delivery window. Configure a window when the workload can tolerate that spread; turn it off when you need the narrowest configured delivery window. Neither setting is an exact-time guarantee. See AWS’s guide to configuring flexible time windows.
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Keep the choice between cron and rate within EventBridge Scheduler for new work. AWS labels older EventBridge scheduled rules as a legacy feature and recommends Scheduler, which it describes as a more flexible and powerful way to manage scheduled tasks centrally at scale. See Setting a schedule pattern for scheduled rules (legacy).
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