WP-Cron runs tasks on a schedule, like cleaning old data, syncing an API or sending a report. It does not use a real server cron. WordPress checks for due tasks when someone visits the site and runs them in the background.

Schedule a daily task

function lotgrafix_schedule_event() {
    if ( ! wp_next_scheduled( 'lotgrafix_daily_task' ) ) {
        wp_schedule_event( time(), 'daily', 'lotgrafix_daily_task' );
    }
}
add_action( 'init', 'lotgrafix_schedule_event' );

function lotgrafix_do_daily_task() {
    // Your code here, for example delete old transients or sync data.
    update_option( 'lotgrafix_last_run', current_time( 'mysql' ) );
}
add_action( 'lotgrafix_daily_task', 'lotgrafix_do_daily_task' );

The wp_next_scheduled() check prevents scheduling the same task again on every page load.

Built in intervals

• hourly
• twicedaily
• daily
• weekly

Create a custom interval

function lotgrafix_cron_schedules( $schedules ) {
    $schedules['lotgrafix_every_fifteen'] = array(
        'interval' => 15 * MINUTE_IN_SECONDS,
        'display'  => __( 'Every 15 Minutes', 'lotgrafix' ),
    );
    return $schedules;
}
add_filter( 'cron_schedules', 'lotgrafix_cron_schedules' );

Then use 'lotgrafix_every_fifteen' as the recurrence in wp_schedule_event().

Run a task only once

wp_schedule_single_event( time() + 60, 'lotgrafix_send_followup', array( $user_id ) );

function lotgrafix_send_followup( $user_id ) {
    // Runs about one minute later.
}
add_action( 'lotgrafix_send_followup', 'lotgrafix_send_followup' );

Remove the task when a plugin is deactivated

function lotgrafix_unschedule_event() {
    $timestamp = wp_next_scheduled( 'lotgrafix_daily_task' );

    if ( $timestamp ) {
        wp_unschedule_event( $timestamp, 'lotgrafix_daily_task' );
    }
}
register_deactivation_hook( __FILE__, 'lotgrafix_unschedule_event' );

Use a real server cron for reliability

On low traffic sites WP-Cron can run late, and on high traffic sites it adds extra requests. Disable it in wp-config.php and call it from the server.

define( 'DISABLE_WP_CRON', true );

*/5 * * * * curl -s https://example.com/wp-cron.php?doing_wp_cron > /dev/null 2>&1

Tip

The free WP Crontrol plugin shows all scheduled events and lets you run them manually while testing.