The honest answer

Sometimes yes, often no, and the only way to know for sure is to test. ISPs get blamed for a lot of packet loss that’s actually happening inside the customer’s home, on their Wi-Fi, or on a server at the far end of the connection. That said, ISPs absolutely do cause packet loss, and when they do, they’re often slow to acknowledge it because the fix usually involves upgrading their own equipment or capacity.

The fair way to think about it is that your ISP is responsible for the journey from their equipment at your exchange to their handoff with the wider internet. They’re not responsible for your Wi-Fi, your router (if you bought it yourself), or the destination server. But they are responsible for everything in between, and that’s a long stretch where things can go wrong.

How to tell if it’s actually them

A traceroute is the single best tool here. Open a command prompt or terminal and run tracert google.com on Windows or traceroute google.com on Mac and Linux. You’ll see a list of hops, each one a piece of network equipment your packets pass through on the way to Google. The first hop is your own router. The second and third are almost always your ISP’s equipment. After that you’re crossing into the wider internet.

If packet loss only appears at hop two or three and stays consistent from there, it’s your ISP. If loss only appears at hop eight or nine and the early hops are clean, the problem is further out and your ISP probably can’t do much about it. If hop one (your own router) is dropping packets, the problem is sitting in your living room.

Run the test several times across different parts of the day. ISP congestion typically shows up in the evening peak between roughly 7pm and 11pm, when everyone on your local network is streaming. If loss is bad at 9pm but clean at 6am, that’s a strong signal of ISP-side capacity issues rather than a hardware fault.

What to do when it is them

Contact support with evidence, not feelings. A screenshot of a traceroute showing 6% loss at their gateway, along with the date and time, gets a different response than “my internet is rubbish.” Ask them to check the line stats from their end, raise a fault, and if they fob you off, ask for the reference number and escalate. In the UK and Ireland you have the right to switch providers without penalty if the service is materially failing to meet what you’re paying for, and reminding them of that tends to focus minds.

Persistent ISP-side packet loss usually points to one of three things: an oversubscribed local exchange (too many customers, not enough capacity), a failing piece of their equipment, or a peering dispute where they’ve under-invested in their connection to another network. The first two get fixed if you push hard enough. The third is harder because it’s a commercial issue and you may need to switch providers if it doesn’t resolve.