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Why is my internet slow when the speed test says it's fast?

It is the most common complaint about home internet, and the most badly answered. You pay for a fast line, the speed test agrees it is fast, and yet calls break up, pages hesitate, and games lag. Here is what is actually happening, in the order it is likely.

Last updated 29 August 2026

Speed is a measure of volume, not of waiting

Megabits per second tells you how much data can move in a second once it is moving. Almost nothing you do all day is limited by that.

Opening a web page is not one transfer. It is forty to eighty small ones — the page, the images, three fonts, an analytics script, a video player, several advert networks — and each unfamiliar name has to be looked up before a single byte of it can be fetched. What you experience as “slow” is usually the waiting between transfers, and a bigger pipe does not shorten a wait.

1. Bufferbloat — the line collapses the moment it gets busy

This is the biggest one and almost nobody tests for it. When a download starts, a cheap router hoards packets in an oversized queue instead of dropping a few, and your latency goes from 10 ms to 300. Everything interactive falls apart, while a speed test running at the same time still reports a perfect number.

The tell: your connection is fine until somebody else in the house starts doing something. If that sounds familiar, it is this.

2. Packet loss — small, invisible, and ruinous

Half a percent of lost packets destroys a voice call and makes a game rubber-band, and it will barely move your speed number. Ordinary speed tests literally cannot see it: they use TCP, which quietly re-sends anything that goes missing, so loss shows up as a slightly lower speed rather than as loss.

Measuring it needs UDP with retransmission switched off, which is why so few tools report it at all.

3. Your DNS resolver is slow

Every new name you visit costs one round trip to a resolver before anything can load. At 8 ms nobody notices. At 150 ms, a page making sixty lookups spends seconds doing nothing but asking questions — on a connection measuring a perfect gigabit.

By default that resolver belongs to your internet provider, and you never chose it. Changing it is free, takes two minutes, and is completely reversible.

4. Wi-Fi, not the line

A very large share of “slow internet” is the last few metres through the air. 2.4 GHz is crowded by every neighbour and every microwave; a wall or two costs more than people expect; and an old device on an old standard can slow a whole band.

The test for this is blunt and takes two minutes: run a test on Wi-Fi, then run it again on a cable. If the numbers are wildly different, stop blaming your provider.

What to do about it

Measure the four things above rather than guessing between them. That is exactly what this site does: it grades bandwidth, latency under load, jitter, packet loss, NAT behaviour and DNS in one run of about ninety seconds, and tells you which one is actually holding you back.