Is my ISP throttling my internet? How to check, step by step
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Your speed test shows 300 Mbps, yet video keeps dropping to low resolution. Or your connection is fine all month and suddenly crawls. Before blaming your provider, it is worth knowing what throttling looks like, because Wi-Fi and network congestion produce very similar symptoms.
What throttling is, and what it is not
Throttling is a deliberate slowdown applied by your provider. It comes in a few forms:
- Per service: video, file sharing or a specific app is limited, while the rest of your traffic runs at full speed.
- After a data cap: once you pass a monthly allowance, your whole line is slowed or deprioritised.
- Plan-based: some plans limit video to a given resolution, which is often written in the contract.
It is not the same as congestion, when too many users share the same equipment at peak hours, or a Wi-Fi problem in your home. Those are far more common. In many countries, rules on an open internet limit what providers may do, and regulators publish how to report abuse.
Step 1: rule out your own network
Run a speed test over an Ethernet cable, next to the router, with other devices paused. Then run our Wi-Fi or line diagnosis. If the cable result is good and only Wi-Fi is slow, the problem is in your home, not at your provider.
Step 2: compare times of day
Test in the morning, mid-afternoon and around 9 pm, three days in a row. A drop that only happens in the evening and affects everything is typical of congestion. A drop that starts on a specific date, often after heavy use, can be a data cap.
Step 3: compare services
Measure the same line with different tools: our test (Cloudflare), Speedtest by Ookla, Fast.com and Google's test. Fast.com downloads from Netflix servers: if it is much slower than the others on the same line, at the same time, video traffic may be treated differently.
Step 4: test with and without a VPN
A VPN hides which service you are using from your provider. Run a test, then switch the VPN on and run it again. A VPN normally makes things a little slower; if the result, or a video's quality, is clearly better with the VPN, your provider may be shaping that traffic. Repeat a few times before concluding.
Step 5: use a dedicated tool
Wehe, a free app developed at Northeastern University and supported by some regulators, replays the traffic of popular apps, then the same traffic disguised, and compares the two. A consistent difference suggests differentiation. One result alone is not proof: run it several times.
Measure your connection now. Start the test
Signs at a glance
| What you see | Most likely cause |
|---|---|
| Only one streaming service is slow | Throttling or a problem on that service's side |
| Everything slows down every evening | Congestion |
| Slow only over Wi-Fi | Your home network |
| Sudden slowdown after heavy use this month | Data cap or fair-use policy |
| Better results over a VPN | Traffic shaping is possible |
What to do if you find throttling
- Read your contract and the provider's traffic management policy: it may be a documented limit.
- Keep dated screenshots of tests with and without VPN.
- Contact your provider's support with that evidence.
- If the answer is not satisfactory, check how your country's telecom regulator handles complaints.
- Compare plans: some providers do not shape traffic at all. Our provider speed tests explain what each major US and UK network should deliver.
If you find no throttling, the usual suspects remain: slow internet causes and fixes and evening slowdowns.
Sources and further reading
Frequently asked questions
Can a speed test detect throttling?
Not on its own. Providers rarely slow down speed-test servers. Comparing several tools, times of day and VPN on or off gives a much better picture.
Is throttling legal?
It depends on the country and the contract. Many places allow reasonable traffic management and data caps but restrict slowing down specific services. Your regulator's website explains the local rules.
Does a VPN stop throttling?
It can stop throttling based on which service you use, because the provider can no longer see it. It does not help against data caps or congestion, and it adds a little latency.
The SpeedFibre team Guides written and reviewed by a telecom engineer specialised in fibre optics (FTTH), with more than 8 years of hands-on network maintenance and measurement. Editorial policy.
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