Start with measurable causes
Do not infer the source from one speed number. Compare the same device, destination and time under controlled conditions.
CONNECTION DIAGNOSIS
Why Is My Internet Suddenly Slow?
A sudden slowdown is usually caused by Wi-Fi interference, competing traffic, a device or router problem, or temporary ISP congestion. Test the connection, then compare Ethernet and Wi-Fi results before changing your plan.
Compare, don’t guess
Pause downloads and test one device. Keep other variables stable, then change one condition at a time.
What can create this pattern
A download, cloud backup or update is using the connection
Confirm this possibility with a repeatable comparison before changing equipment or service.
Wi-Fi interference or a weak signal changed the local link
Confirm this possibility with a repeatable comparison before changing equipment or service.
The router, modem or device needs attention
Confirm this possibility with a repeatable comparison before changing equipment or service.
Congestion or an outage is affecting the ISP path
Confirm this possibility with a repeatable comparison before changing equipment or service.
Test it in this order
Pause downloads and test one device
Record the result, keep the test comparable and continue only after this step.
Run the same test over Ethernet
Record the result, keep the test comparable and continue only after this step.
Restart network equipment once
Record the result, keep the test comparable and continue only after this step.
Repeat at another time and record the results
Record the result, keep the test comparable and continue only after this step.
Narrow down what changed
Record the device, connection type, time, download, upload and response timing. Change one condition at a time. These patterns suggest the next check; they do not prove which component is faulty.
| What you observe | What to investigate | Next step |
|---|---|---|
| Ethernet is consistently faster than Wi-Fi on the same device | Wireless signal, interference, band or local contention | Compare Wi-Fi near the router and in the affected room |
| Only one device is slow in the same location | Device load, software or its connection | Compare another device and browser |
| Multiple wired devices slow down at similar times | Shared traffic, router load or the provider path | Record quiet-hour and busy-hour tests |
| Speed looks normal but calls or games lag | Upload demand, variable timing or latency under load | Check the signals beyond download speed |
Run a Wi-Fi versus Ethernet experiment
- Use one device near the router and pause large background transfers.
- Run two or three checks over Wi-Fi, noting the range of results.
- Connect by Ethernet, turn off Wi-Fi on that device and repeat with the same test.
- Repeat the comparison later. Save the results and conditions before contacting support.
If your internet became slow all of a sudden, compare the same device and endpoint before and after each change. The homepage connection check can compare the previous and current result in the same tab. Keep the tab open when you change connection type. A local Docker preview measures the local endpoint, so use the public site to investigate an internet connection.
If comparable wired results degrade across several apartments, review the MDU broadband guide for multi-dwelling units before escalating the shared building connection.
Full home-testing guide → · How to interpret browser measurements →
Use more than download speed
Read throughput together with ping, jitter and packet loss. A browser result describes this device, route and moment; it does not by itself prove an ISP fault.
Continue the diagnosis
speedtest network quality packet lossFrequently asked questions
Why Is My Internet Suddenly Slow?
A sudden slowdown is usually caused by Wi-Fi interference, competing traffic, a device or router problem, or temporary ISP congestion. Test the connection, then compare Ethernet and Wi-Fi results before changing your plan.
What should I test first?
Pause downloads and test one device. Compare download, upload, latency, jitter and packet loss—not download alone.
Does one test prove the cause?
No. Repeat comparable tests over Ethernet and Wi-Fi, on more than one device and at different times.
MEASURE BEFORE YOU CHANGE
Start connection test →Find where the connection slows down
Save the result, repeat under comparable conditions and use the difference as evidence.