How to track data usage on your Mac

The quick answer

macOS has no daily or monthly data counter. What it has is a running total per network interface since the last boot. Activity Monitor shows it at the bottom of the Network tab (“Data received” and “Data sent”), and Terminal shows it per interface:

netstat -ib | awk 'NR==1 || /<Link#/'

Name  Mtu   Network    Address            Ipkts Ierrs     Ibytes    Opkts Oerrs     Obytes
en0   1500  <Link#14>  a4:83:e7:..:..:..  9123411     0 11834226311 4401229    0 1290112044

Ibytes is downloaded and Obytes uploaded, in bytes. Divide by 1,000,000,000 for GB. en0 is usually Wi-Fi on a MacBook; lo0 is loopback (your Mac talking to itself) and doesn’t count toward any cap.

To check which name is which:

networksetup -listallhardwareports

Turn it into a daily total

Because the counters reset at reboot, the trick is to record them and subtract. Save this as ~/bin/datalog.sh:

#!/bin/bash
# Appends date, rx bytes, tx bytes for en0
netstat -ib -I en0 | awk -v d="$(date '+%F %T')" \
  '/<Link#/ {print d, $7, $10; exit}' >> ~/datausage.log

Run it at the start and end of the day (or every hour from cron or a launchd agent) and subtract consecutive lines. Watch for a smaller number than the line before: that’s a reboot, so start counting again from zero.

It’s rough but it works for a week on a hotspot. For something you’ll leave running for months, a tool that stores daily totals is less fiddly.

Which app used it

Per-interface totals tell you how much. For who, sort processes by bytes:

nettop -P -L 1 -J bytes_in,bytes_out -x | sort -t, -k2 -nr | head

Or open Activity Monitor › Network and sort by Rcvd Bytes. The full walkthrough, including browser helpers and system daemons, is in which app is using my network.

The usual data hogs

• macOS updates: several GB each. System Settings › General › Software Update › ⓘ next to Automatic Updates, then turn off “Download new updates when available” while on a metered connection.
• iCloud Photos and iCloud Drive: a new batch of photos or a large folder change can upload gigabytes. Pause from the Photos app settings.
• Background downloads: nsurlsessiond fetches for the App Store and many apps. See nsurlsessiond.
• Docker image pulls and package installs: docker pull, npm install and Homebrew updates can be hundreds of MB each.
• Streaming and video calls: an hour of HD video is roughly 1–3 GB.

Save data on a hotspot

1. Connect to the hotspot and turn on Low Data Mode: System Settings › Wi-Fi › Details next to the network › Low Data Mode. macOS pauses many background tasks, and well-behaved apps hold off too. macOS usually remembers it for iPhone hotspots.
2. Pause sync apps from their menu bar icons.
3. Quit apps you aren’t using; chat apps and browsers with many tabs poll constantly.
4. Check the iPhone side too: Settings › Cellular (or Mobile Data) › Personal Hotspot shows what the hotspot has used this period.

Seeing it over time

Stat Space records the bytes on each physical interface (Wi-Fi, Ethernet, iPhone USB) once a minute and keeps daily totals for 90 days. Its History section shows today, this month and a 30-day bar chart per interface, so “how much did I use on the hotspot this week” is one glance. It’s free and stays on your Mac; it costs one wake-up a minute, shared with the rest of its history.

It doesn’t know your billing cycle or your cap, and its totals are for this Mac only. Seeing how much each app used is the Pro Network by app section.