When using Boot Camp in macOS, you may get a “The startup disk does not have enough space to be partitioned”
The error additionally displays “You must have at least 40 GB of free space available.” below that.
Enough Free Space
It would make sense if there wasn’t enough free space on the startup disk but in my case for example, I have more than enough space:
How to Fix “The startup disk does not have enough space to be partitioned”
The culprit is the macOS Time Machine software causing the error message.
Resolving the problem is quick and easy, follow these steps:
1. Turn Off Time Machine
First go to System Preferences > Time Machine.
Turn off “Back Up Automatically” and also remove the backup disk from Time Machine. Your Time Machine should look like this:
2. Thin Local Snapshots
In addition to turning off Time Machine, you also need to thin your local snapshots.
Open your Terminal and type or paste the following command:
sudo tmutil thinlocalsnapshots / 999999999999
Type in your administrator password when prompted and hit Enter/Return to continue.
When it finished running, you can reopen Boot Camp Assistant and try again, it should work fine now.