A scheduled backup did not start

What to check, in order

Is the program running? Its icon should be by the clock (see “The program window and the icon by the clock”). If it is not there, start the program and turn on starting at sign-in (see “Starting the program at sign-in”).
Are scheduled backups paused? Check the menu of the icon by the clock: “Pause scheduled backups” must not be ticked.
Does the template have a schedule? On the “Templates” page, select the template. The “Schedule:” field must not be set to “Manually”, and below it the program says when the backup will start (for example “Next backup: …”).
Was the backup drive connected? A daily backup waits for the drive and starts as soon as it is connected. A “When the destination drive is connected” backup starts at most once every 12 hours.
Did a notification arrive? A notification that the backup did not start because the template is encrypted and the password is not remembered: remember the password (see “Encrypting a backup”). “The scheduled backup failed” or “Scheduled backup paused”: the notification says what happened.
Was the computer off or asleep, or the account signed out? A backup whose due time has passed starts once after the computer is switched on and you sign in.
Was the schedule changed today? A new time applies from the next due time: setting 20:00 at 21:00 means the first backup tomorrow.

There is one attempt per due time. If it failed, the next one comes at the next due time. To avoid waiting, start the backup manually: “Run backup” on the “Templates” page or “Back up now” in the menu of the icon by the clock.
When another operation, for example a restore, is running at the due time, the scheduled backup starts after it finishes.
When a template with a schedule has not made a successful backup for 7 days, the program reminds you with a notification once a day.

Everything looks fine, but the backup still does not start: look in the log (see “Where to find details: the program log”) and check whether, at the due time, the program recorded starting the scheduled backup and what happened after that.