Mac storage basics · Time Machine basics
What happens when my Time Machine drive is full?
Short answer: It deletes the oldest backups to make room and tells you. History gets shorter but recent backups stay; if one backup won't fit at all, use a bigger drive or exclude folders.
Time Machine automatically deletes the oldest backups to make room for new ones, and tells you when it does. Recent backups are kept; the history simply gets shorter.
If a single backup is bigger than the whole drive, backups stop and you'll need a larger drive or to exclude some folders. Time Machine keeps hourly backups for 24 hours, daily backups for a month and weekly backups for older months, as space allows.