L modifier in the day-of-month field. To run on the last day of every month at midnight UTC: cron(0 0 L * ? *). The expression has six fields (minute, hour, day-of-month, month, day-of-week, year), the day-of-week is ?, and the year defaults to *.View future cron matches in a calendar
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cron(0 0 L * ? *) — midnight UTC on the last day of every month.cron(0 12 L * ? *) — noon UTC on the last day of every month.cron(0 0 L 12 ? *) — midnight UTC on December 31st only.cron(30 23 L 1,4,7,10 ? *) — quarterly: last day of January, April, July, October at 23:30 UTC.cron(0 9 L * ? 2026) — last day of every month in 2026 only.Resources:
MonthEndRule:
Type: AWS::Events::Rule
Properties:
Description: "Run last day of every month at 00:00 UTC"
ScheduleExpression: "cron(0 0 L * ? *)"
State: ENABLED
Targets:
- Arn: !GetAtt MonthEndLambda.Arn
Id: MonthEndLambdaTarget
MonthEndPermission:
Type: AWS::Lambda::Permission
Properties:
FunctionName: !Ref MonthEndLambda
Action: lambda:InvokeFunction
Principal: events.amazonaws.com
SourceArn: !GetAtt MonthEndRule.Arnimport * as events from 'aws-cdk-lib/aws-events';
import * as targets from 'aws-cdk-lib/aws-events-targets';
new events.Rule(this, 'MonthEndRule', {
schedule: events.Schedule.expression('cron(0 0 L * ? *)'),
targets: [new targets.LambdaFunction(monthEndLambda)],
});For the newer EventBridge Scheduler with timezone support:
import * as scheduler from 'aws-cdk-lib/aws-scheduler';
new scheduler.CfnSchedule(this, 'MonthEndSchedule', {
scheduleExpression: 'cron(0 0 L * ? *)',
scheduleExpressionTimezone: 'America/New_York',
flexibleTimeWindow: { mode: 'OFF' },
target: { arn: monthEndLambda.functionArn, roleArn: schedulerRole.roleArn },
});cron(0 0 L * ?) is invalid; you need the trailing year (* for any).Yes. AWS EventBridge cron expressions accept `L` in the day-of-month field. Use `cron(0 0 L * ? *)` for midnight UTC on the last day of every month. AWS cron has 6 fields (minute, hour, day-of-month, month, day-of-week, year) — note the year field is required.
AWS EventBridge follows the Quartz convention: you cannot specify both day-of-month and day-of-week as values. Exactly one must be `?` (no specific value). When you constrain day-of-month with `L`, the day-of-week field must be `?`.
By default, all cron expressions run in UTC. To run in a specific timezone, use the EventBridge Scheduler (newer service) which accepts a `ScheduleExpressionTimezone` parameter. Older EventBridge Rules are UTC-only — you have to convert your local time to UTC manually.
EventBridge Rules is the original service (still supported). EventBridge Scheduler is the newer, dedicated scheduler with timezone support, one-off schedules, and higher throughput. Both accept the same cron syntax (`cron(...)`), and both support `L`.
AWS EventBridge does not support `W` or `LW`. To run on the last weekday of the month, schedule daily and check the weekday at runtime in your Lambda — `event.time` plus `Date.prototype.getDay()` is enough.
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