TimeMachine going backwards?

[Sonic42]

i've had Time Machine running for the past 2 months. it seems like it is working, my backup drive started at 500GB free and every day has slowly gone down in size until it had about 275GB remaining, then it started to go back up in size. now my time machine disk has 290GB remaining.

any ideas on why Time Machine would start using less and less disk space?

thanks!

 

[erickkoch]

I can't be sure but my theory is that you have been changing fewer files recently so there is less to back up and you may have deleted large files since your initial backup that are now being deleted in increments so the files sizes shrink.

As I understand it, Time Machine backs up files that have been changed or added. As you delete files I think (please correct me if I'm wrong) they get deleted on the incremental backups as well. You'll have to go back further in time to retrieve deleted files.

Anyone else have other ideas?