Mac 'Your Startup Disk Is Almost Full' Warning

The macOS 'Your startup disk is almost full' warning means the system drive has very little free space, which can cause performance issues and crashes. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: macOS needs at least 10-15 GB free for swap, caches, and updates. Performance degrades significantly when disk is over 90% full. macOS may fail to boot if the disk is completely full. Virtual memory (swap) requires free disk space to function. System updates require substantial free space (12-35 GB). Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: Large files accumulated (videos, photos, downloads). Application caches and logs consuming space. Time Machine local snapshots filling up the drive. Xcode and iOS simulators consuming tens of GB. Mail attachments and iMessage media stored locally. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Check storage: Apple menu > About This Mac > Storage (or System Settings > General > Storage on Ventura+). Empty Trash: right-click Trash icon > Empty Trash. Delete Time Machine local snapshots: tmutil listlocalsnapshots / then tmutil deletelocalsnapshots [date]. Clear application caches: ~/Library/Caches/ (delete contents, not the folder). Use Finder > Go > Go to Folder > ~/Downloads and delete old downloads. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our Mac Error Codes collection on Error Codes Wiki. We provide comprehensive, up-to-date information to help you find solutions quickly.