Why is my Mac using so much data? The usual background culprits
What uses data in the background on a Mac: iCloud, Photos, updates, browsers and backups, and how to spot and slow each one.
What uses so much data on a Mac?
Background sync and downloads: iCloud Photos and Drive uploading, macOS and App Store updates downloading, browsers loading video and refreshing tabs, and cloud backup apps.
How do I find what is using data right now?
Activity Monitor, Network tab, sorted by Sent or Received Bytes. nsurlsessiond high in the list means a background download or upload for an app or iCloud: nsurlsessiond explained.
Why is my Mac uploading so much?
Usually iCloud Photos or iCloud Drive syncing new files, or a backup service. Pausing Photos sync or turning on Low Data Mode for that network stops most of it.
Common questions
Why is my Mac using data when I am not using it?
Background sync and updates: iCloud, Photos, macOS and App Store downloads, and browsers refreshing tabs.
How do I stop my Mac using data in the background?
Turn on Low Data Mode for the network in Wi-Fi settings and pause iCloud Photos while on a hotspot.