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What is using data on my Mac?
Open Activity Monitor → Network and sort by Rcvd Bytes to see which apps and processes used the most data since your last restart. The usual culprits are system updates, iCloud sync (cloudd, bird, nsurlsessiond), cloud drives and browsers. To see when and on which network it happened, track your usage with Byter.
Your data is disappearing and you’re not even streaming anything. Here’s how to find the cause.
Step 1: Look in Activity Monitor
- Open Activity Monitor (Command + Space, type “Activity Monitor”).
- Click the Network tab.
- Click the Rcvd Bytes column so the biggest downloaders are at the top. Sent Bytes shows uploads.
Names you’ll often see near the top: nsurlsessiond (background downloads for apps and iCloud), cloudd and bird (iCloud sync), softwareupdated (macOS updates), and your browser. What each one does: Mac processes that use data, explained.
Step 2: Check what happens when you’re idle
Leave your Mac alone for 15 minutes on your hotspot, then check again. If the totals jumped, something is downloading in the background, usually an update or a sync.
Step 3: Track it over time
Activity Monitor resets when you restart and mixes every network together. Byter keeps a history of your usage on each network, so you can see that, say, 1.2 GB went through your hotspot between 2 and 3 pm. Byter also sends a heads-up when your usage is unusually high, plus daily, weekly and monthly summaries.
Step 4: Stop it
Turn on Low Data Mode for your hotspot, pause updates and cloud sync. All the steps: how to reduce data usage on a Mac.
Questions
Why is my Mac using data when I’m not using it?
Background tasks: macOS and app updates, iCloud Photos and iCloud Drive sync, cloud drives such as Google Drive and Dropbox, and browser updates.
Can I see data usage per app on a Mac?
Yes, in Activity Monitor’s Network tab, since the last restart. For per-network history, use Byter.