Why Is My Upload Speed Slow?

Understanding Why Upload Is Slow

Slow upload has different causes depending on whether it's always been slow or just started — and whether it's slow on all devices or just one.

Cause 1: Your Internet Plan Has Slow Upload by Design

Cable internet — the most common type in the US — uses asymmetric technology. A typical cable plan looks like this:

If your measured upload matches the upload column of your plan, there's nothing wrong — that's the plan limit. The fix is to upgrade to a plan with more upload, or switch to fiber for symmetric speeds.

Cause 2: Background Apps Are Consuming Upload

Cloud services upload constantly in the background. Check which apps are using your upload bandwidth before assuming your ISP is the problem.

Windows: Task Manager (Ctrl+Shift+Esc) → Performance → Open Resource Monitor → Network tab. Sort by "Send (B/sec)".

macOS: Activity Monitor → Network tab. Sort by "Sent Bytes."

Suspend or limit: Backblaze, iCloud, Dropbox, OneDrive, Google Drive, Windows Update (delivery optimization), and any active torrent clients. Run the speed test again with these paused.

Cause 3: WiFi Is the Bottleneck

WiFi's half-duplex nature hurts upload more than download. Your device's WiFi transmit power is lower than the router's receive sensitivity, meaning upload range is shorter than download range. If you're more than 15 feet from the router or have walls between you and it:

• Connect via Ethernet and retest — if upload doubles, WiFi was the bottleneck.
• Move closer to the router and test — upload should improve significantly.
• Check for WiFi interference that might be affecting your channel.

Cause 4: ISP Upload Throttling

Some ISPs throttle specific types of upload traffic — particularly P2P file sharing and large sustained uploads. To test if your ISP is throttling upload:

1. Run a speed test on SpeedTestHQ and note your upload speed.
2. Connect a VPN using WireGuard protocol and run the same test.
3. If upload speed improves significantly with the VPN, your ISP is throttling that traffic type.

See our full guide on detecting ISP throttling.

Cause 5: Router or Modem Issue

A router or modem that needs a restart can develop asymmetric performance degradation — affecting upload more than download. Restart both devices (modem first, then router) and retest. If the issue appeared recently and restarting fixes it temporarily, check for a firmware update for your router.