Are Windows Backups Cumulative or Incremental?

I want to free some space used by Windows Backup, but I don't want to lose backed up files in the process.  The program explains that I can indeed remove old backups to save space here:

However, it does not tell me if removing old backups will also remove files that hadn't changed since that backup was made. The file sizes do get smaller over time, so that makes me believe these are incremental... but there's no way I added 75GB of new files in October -- I was away on a business trip most of that period.  So, how can I know for sure before I delete old backups?



Hi Shawn,


Backups are created in sets known as backup periods. To help maximize your disk space, Windows Backup backs up all selected folders the first time it runs and then it only backs up files that are new or have been modified since the last backup was made.


Periodically, Windows creates a new, full backup. Each full backup is known as a backup period. When you view your file backups, you see all of the backup periods labeled with date ranges. If you decide to delete file backups, you should always keep the most recent file backup.


The decrease or increase in size of the backup file can have many reasons; it could be due to the programs and data files that you have deleted\added. Also the temporary internet files add to the size of the data files accessed during the period of the backup taken.


For more information on Backup:

Back up and restore: frequently asked questions

What backup settings should I use to maximize my disk space?



Syed N – Microsoft Support
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Last updated July 7, 2021 Views 1,925 Applies to: