Why is my Mac storage filling up by itself?

Updated November 3, 2026

You didn't download anything big, yet free space keeps dropping: a few GB this week, a few more next week.

The short answer: it's rarely one big file. It's a handful of things that grow without asking: local Time Machine snapshots, app caches, swap, chat app media, iPhone backups, Photos and iCloud downloads, and developer tools. System Settings › General › Storage shows today's total, not what changed, so measure twice and compare.

What grows on a Mac by itself?

How do I find what's growing?

Save the size of every folder in your home and your Library to a file, with today's date:

du -sk ~/* ~/Library/* ~/Library/Containers/* ~/Library/Group\ Containers/* 2>/dev/null > ~/du-$(date +%F).txt

Run the same command again a few days or a week later. Then compare the two files (put in their dates) to list every folder that grew by more than 100 MB, biggest first (a folder that grew shows up together with the folders it's in, such as ~/Library):

awk -F'\t' 'NR==FNR{a[$2]=$1;next} $1-a[$2]>100000 {printf "%d MB\t%s\n", ($1-a[$2])*1024/1e6, $2}' ~/du-2026-11-01.txt ~/du-2026-11-08.txt | sort -rn

Give Terminal Full Disk Access first (System Settings › Privacy & Security › Full Disk Access), or some folders are counted as empty.

Why does free space go up and down on its own?

Part of what's used is purgeable: snapshots, offline iCloud copies and caches that macOS removes when it needs room. So free space can drop for days and jump back after a restart or a large download, without you doing anything.

How do I stop it from filling up again?