WiFi Slow After macOS Update? 7 Fixes for Mac Users

You installed the latest macOS update and now your WiFi feels sluggish. Downloads crawl, video calls stutter, and pages take noticeably longer to load — yet your iPhone on the same network is fine. This is one of the most common Mac complaints after every major release, and it has several well-documented causes. Here are seven targeted fixes, ordered from quickest to most involved.

Why Does macOS Slow Down WiFi After an Update?

Several things happen in the background immediately after a macOS upgrade:

Spotlight re-indexes your entire drive. The mds and mds_stores processes consume heavy CPU and I/O, which starves the mDNSResponder DNS resolver of resources.
iCloud, Time Machine, and background app updates all start simultaneously, competing for your bandwidth.
Network preference files can be left in an inconsistent state, causing your Mac to use incorrect MTU values, wrong proxy settings, or a stale DHCP lease.
Sonoma and Sequoia introduced “Limit IP Address Tracking,” which routes traffic through Apple’s relay proxy for privacy — adding latency and reducing throughput for many users.
macOS 15.0 (Sequoia) changed the network extension API, which broke several third-party VPN and firewall apps and caused severe intermittent slowdowns until Apple patched it in 15.0.1.

Knowing the cause tells you exactly where to look. Work through the fixes below in order.

Fix 1: Check Whether Spotlight Is the Culprit

Before changing any network settings, open Activity Monitor (Applications → Utilities → Activity Monitor) and sort by CPU %. If mds or mds_stores are near the top, Spotlight indexing is consuming system resources — and your network slowdown will resolve on its own once indexing completes, usually within one to three hours on an SSD Mac.

To confirm the status from Terminal:

mdutil -s /

If you need the speed back immediately, you can pause indexing temporarily:

sudo mdutil -a -i off

Re-enable it when you’re done:

sudo mdutil -a -i on

Fix 2: Disable “Limit IP Address Tracking”

This Sonoma and Sequoia feature routes your traffic through Apple’s iCloud Private Relay infrastructure, which measurably reduces throughput. Many users report this single toggle restoring their full speed.

Go to System Settings → Network → Wi-Fi → Details… → scroll down to “Limit IP Address Tracking” → toggle it OFF.

Also check Safari: Safari → Settings → Advanced → uncheck “Use advanced tracking and fingerprinting protection” if you notice speed issues specifically in the browser.

Fix 3: Renew Your DHCP Lease

Your Mac might still be holding a DHCP lease that was assigned before the update, which can cause routing conflicts. Renewing it is instant and risk-free.

Go to System Settings → Network → Wi-Fi → Details… → TCP/IP tab → click “Renew DHCP Lease.”

Your Mac will request a fresh IP address from your router. If a lease conflict was causing the slowdown, you’ll notice the improvement within seconds.

Fix 4: Flush the DNS Cache

The mDNSResponder DNS cache persists across reboots and can carry stale or corrupt records after an OS upgrade, causing slow or failed domain resolution. Open Terminal and run:

sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

No output means success. Test your speed again — this fix alone resolves many post-update slowdowns where pages load slowly but downloads at speed.

Fix 5: Change Your DNS to Google or Cloudflare

If flushing the cache helped temporarily but the problem returns, your ISP’s DNS servers may simply be slow or unreliable. Switching to a public DNS is a permanent fix.

Go to System Settings → Network → Wi-Fi → Details… → DNS tab. Click + and add 8.8.8.8 and 8.8.4.4 (Google) or 1.1.1.1 and 1.0.0.1 (Cloudflare). Remove the existing ISP-assigned entries using the – button, click OK, and Apply. Then flush the DNS cache again (Fix 4) to clear any cached ISP records.

Fix 6: Delete Corrupted Network Preference Files

macOS upgrades sometimes leave the network plist files in /Library/Preferences/SystemConfiguration/ in an inconsistent state, causing wrong MTU values, phantom proxy settings, or adapter misconfigurations. Deleting them forces macOS to generate clean versions on the next boot.

In Finder, press Command+Shift+G and navigate to:

/Library/Preferences/SystemConfiguration/

Move these three files to your Desktop as a backup (do not delete permanently until you confirm the fix works):

com.apple.airport.preferences.plist
NetworkInterfaces.plist
preferences.plist

Restart your Mac. macOS will recreate all three files with factory-default settings. You will need to rejoin your WiFi network and re-enter the password.

Fix 7: Run Wireless Diagnostics

If the problem persists, use Apple’s built-in tool to identify signal, interference, and channel issues. Hold the Option ( ⊕ ) key and click the Wi-Fi icon in the menu bar, then select “Open Wireless Diagnostics…”

Click Continue to run the automated scan. After it completes, open the Window menu inside the app to access the Scan panel (which shows all nearby networks and their channels) and the Performance panel (which graphs signal strength and noise over time). If the scan flags channel congestion or interference, log into your router and switch to the recommended channel. For a walkthrough on changing channels, see our guide on how to change your WiFi channel.

Quick Summary

Try these fixes in order: check Spotlight first (wait it out if indexing), disable Limit IP Address Tracking, renew your DHCP lease, flush DNS, switch to Google or Cloudflare DNS, delete network plist files, and finally run Wireless Diagnostics. Most users find their issue is resolved by Fix 2 or Fix 4. If you’re still experiencing problems, it may be a broader network issue — run a speed test to check your actual throughput and compare it to your ISP plan. For persistent slow speeds across all devices, see our guide on why your WiFi is slow.