It's one of the most common internet frustrations: you pay for 300 Mbps, you run a test, and you see 180. Is your provider cheating you? Usually not — some gap between your plan and your real speed is normal and expected. But there's a line between a normal gap and a real problem, and this guide shows you where it is, what causes the loss, and how to pin down exactly where your speed is disappearing.
The big reason: 'up to' speeds
Providers almost always advertise speeds as 'up to' a number, with fine print that the speed isn't guaranteed. That advertised figure is a best-case peak, measured to your router under ideal conditions — not a constant speed delivered to every device in your home. Internet providers are largely in the clear legally if you don't hit the maximum, because the contract typically only promises 'up to.'
Why they word it this way: the speed that actually reaches you depends on factors the provider doesn't fully control — your home wiring, the distance from your home to their local cabinet, how many neighbors share your line, and your own equipment. So the headline number is the ceiling, not the floor.
A useful benchmark: on a wired test with other devices idle, getting 80–90% of your advertised speed is healthy and normal. Consistently getting far below that — say half or less — is when it's worth investigating or calling your provider.
Where your speed actually goes
Between your provider's advertised peak and the number on your screen, several things take a cut. In rough order of how much they typically matter:
1. Wi-Fi instead of a wired connection
This is the biggest culprit for most people. Wi-Fi signal weakens with distance, walls, and interference from neighbors and appliances, and the bandwidth is shared among everything connected wirelessly. A device three rooms from the router can easily see half the speed — or less — that a wired connection in the same house gets. Wi-Fi loss is normal physics, not a fault.
2. Peak-hour congestion
On cable and other shared connections, speed drops in the evening (roughly 7–11pm) when your whole neighborhood is online drawing from the same local capacity. Your midnight speed and your 9pm speed can be very different. This is normal for shared connection types and largely unavoidable without switching to a less-contended technology like fiber.
3. Other devices and people using the line
Your connection is split across everything using it. A 4K stream, a game download, a cloud backup, or a housemate's video call all consume bandwidth that's then unavailable to your test. The more simultaneous users, the less each gets — like more people drawing from the same well.
4. Old or underpowered hardware
An aging modem or router can cap your speed below your plan. Older equipment may not support newer standards or gigabit throughput. If you upgraded your plan but your speed didn't rise, your hardware is a prime suspect — the device, not the line, is the bottleneck.
5. Wiring and the 'last mile'
The final stretch of connection between your provider's local hub and your home — old copper, a loose coaxial connector, buried cable, the utility pole — is often the weakest link. Problems here cap your real speed regardless of how fast the backbone beyond it is.
6. Protocol overhead
A small, unavoidable slice goes to network overhead — the protocol headers and signaling that make data transfer work. This is why even a perfect wired test usually reads slightly under the rated line speed. It's a few percent, not a major loss, but it's part of why you never see exactly 100%.
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Run a speed testThe Mbps vs MB/s trap
One 'slow speed' complaint is actually a misunderstanding. Internet speed is measured in megabits per second (Mbps), but file downloads are often shown in megabytes per second (MB/s). A byte is eight bits, so your download manager shows a number roughly one-eighth of your Mbps speed.
So on a 100 Mbps connection, a download showing '12.5 MB/s' is exactly right — that's full speed, not a slowdown. If your downloads look like one-eighth of your plan, your connection is working perfectly and you're just reading two different units.
How to find where the loss happens
To pin down whether the problem is your provider, your hardware, or your Wi-Fi, test at different points in your network. Work through these in order:
- Test wired, straight from the modem. Connect a computer to the modem (or gateway) with an Ethernet cable, with the router and other devices out of the picture. This shows the raw speed arriving at your home, closest to what your provider actually delivers.
- Compare to your plan. If this wired test is within 80–90% of your advertised speed, your provider is delivering and the loss is happening inside your home. If it's far below, the issue is upstream — your provider, hardware, or wiring.
- Then test over Wi-Fi, in the spot where you actually use your devices. A big drop between wired and wireless means Wi-Fi is your bottleneck — distance, interference, or an old router.
- Test at different times of day. If speed is fine at midday but tanks at 9pm, you're seeing peak-hour congestion rather than a hardware fault.
- Keep timestamped records. If you consistently get far below your plan on a wired test across several days, that log is your evidence when you contact your provider.
When it's actually your provider's problem
It's likely an issue worth raising with your provider when: a wired test from the modem consistently comes in far below your plan (not just a little under), the shortfall persists across different times of day rather than only at peak, and it doesn't improve after restarting your equipment. At that point, document the results with timestamps, reference your plan's advertised speed, and contact them — a persistent, well-documented gap is what gets a technician dispatched or a line issue fixed.
Before you call: restart your modem and router, and confirm you're testing wired. Those two steps resolve or explain a large share of 'slow internet' cases, and your provider will ask you to do them anyway.