Time machine says not enough space to perform a backup.

deborah 128 wrote:

I need some help with troubleshooting why time machine keeps saying there is not enough disk space to perform backups. This started occurring after having taken my laptop on vacation then returning home. I tried removing, then reselecting the disk in preferences. Rebooted too, nothing. What next?

See if this solves your problem—

"The backup disk is full" or ". . . almost full"

or "This backup is too large . . ."

https://www.baligu.com/pondini/TM/C4.html

additionally—

Time Machine: How to transfer backups from a current backup drive to a new backup drive

https://support.apple.com/en-us/HT202380

Types of disks you can use with Time Machine on Mac - Apple Support

Caution: DO NOT attempt to manually delete anything off your Time Machine drive. Those files are all not removable, and can not be deleted. They may move to the Trash, but will not free up any space, and will continue to be not removable.

How much stuff is on your Boot drive?

how large is your backup drive?

How much of (2TB less 18GB) is taken up by random files and is therefore not available for backups? If there are random files, where are their backups being stored?

You may need to acquire a large external drive, or expand your Time Capsule drive, or both. Luckily, external drives are cheap these days.

If Time Machine had more space, it could consolidate your older backups to make more space available. It routinely does this in a way that eliminates the oldest backups,, but maintains a copy of every file still present on your Mac.

The message that there is not enough space is the hint that it cannot continue to consolidate backups, but you need to make more room.