Minimum fiber speed: is it guaranteed in Belgium?

No. The speed on the billboard is guaranteed by no Belgian provider, fiber included. Two other figures are: the minimum speed and the normally available speed written into your contract for your address. They are almost always lower, rarely read, and yet they are the only ones a complaint can rest on.

The advertised speed is guaranteed nowhere

Let us start with the thesis, since it runs against intuition. When Proximus sells Internet Mega Fiber at 500 Mbps download, or when Telenet advertises 2.5 Gbps, the provider does not promise you will get that speed. It promises that your line is configured to reach it under the best conditions, and it commits, alongside, to more modest values that regulation forces it to publish. The distinction is no lawyer's trick: it follows from how a fiber network is built. You can read it in black and white in the contract documents.

The contract summary Proximus publishes for its fiber offers, the one for Internet Fiber Start for instance, is the clearest illustration. The "min", "normally available" and "max" boxes are there, but empty: they all point to a speed page calculated address by address. Same product, same price, three different figures depending on the street.

Which speeds must your contract state?

Four, for a fixed connection, each in both directions.

Article 4 of the EU open internet Regulation 2015/2120 requires providers to explain the minimum, normally available, maximum and advertised speed; our guide to testing your speed properly covers the definitions in detail. The key point is the clarification made by BIPT, the Belgian telecom regulator (IBPT in French), in its decision of 2 May 2017 on communicating broadband speed: the normally available speed is the one you must get at least 95% of the time. Here is what that ladder looks like on a real line.

The right-hand column comes from a Proximus subscriber's speed sheet posted on the provider's official forum in February 2021. It was a VDSL line, not fiber, but it shows the full ladder: 100 Mbps sold, 62.4 Mbps guaranteed, a floor at 62% of the advertised figure.

On a true FTTH (fiber to the home) line, the gap between these values is much tighter, since distance to the exchange no longer degrades the signal. It does not vanish, though.

Why no provider guarantees the maximum on fiber

Because the fiber entering your home is shared.

Belgium's FTTH network relies on passive optical networks: a single beam leaves the exchange and is split, by a coupler, between 32 or 64 homes. GPON carries 2,488 Mbps downstream for the whole group; XGS-PON, its successor, 9,953 Mbps. Divide, and you get the worst case, the one where every neighbour downloads flat out at the same instant.

Nicolas's calculation from ITU-standardised capacities. Shares are raw speeds, before protocol overhead; the Proximus catalogue was checked on its internet subscriptions page on 20 September 2026.

The table says one simple thing. A provider selling 500 Mbps on a 64-way coupler sells about thirteen times what it could deliver to each home if everyone used it at once. That is not a scam, it is pooling, exactly as a motorway is not built for every car in the country to drive on it in the same minute. But it makes guaranteeing the maximum impossible by design. Hence the duty to state a floor and a "normal" value, the only promises that can be kept.

Is fiber therefore less guaranteed than cable?

That is the serious objection, and it deserves an honest answer: no, quite the opposite.

Coaxial cable also shares its capacity between neighbours, on a local segment, and it is the one with the most visible evening dips between 8pm and 11pm. VDSL weakens with every hundred metres of copper, which explains floors at 60% of the advertised speed as in the table above. Fiber combines real sharing with a huge margin: even in the GPON worst case, 39 Mbps per home still carries a 4K stream, and the worst case does not happen in real life.

There is a nuance, though. Telenet itself states that a subscriber to the 2.5 Gbps tier whose address cannot support it yet automatically gets the fastest available speed, 1 Gbps, with the upgrade following the network. The product sold and the speed delivered can therefore differ from day one, contract in hand. Orange, for its part, publishes ceilings as ranges, 150 to 200 Mbps or 400 to 500 Mbps depending on the plan, on its speed help page, checked on 26 September 2026.

Is there a legal minimum speed in Belgium?

Yes. It probably does not concern you.

The Royal Decree of 10 September 2023, published in the Belgian Official Gazette on 26 September 2023, sets the universal service download speed at 10 Mbps, raised to 30 Mbps on 1 January 2027. That speed must be delivered every day, at any hour, except for one hour a day at most. The text itself states that it creates no "immediate right": a universal service provider must first be designated, and the request must be reasonable and concern the main residence.

The decree's figures frame the issue. When it was drafted, 99.4% of Belgian households were covered at 10 Mbps and 99.1% at 30 Mbps by a wired network; the floor therefore targets about 46,000 households, mostly in the least densely populated areas. Fiber geography follows the same slope. In mid-2026, FTTH passed roughly 78% of homes in Brussels, 71% in Flanders and 44% in Wallonia. A fiber household in Brussels or Flanders is very far from the legal floor; an isolated Walloon home still on long copper may be close to it, and that is who the Walloon "Last Mile" call for projects and the supported rollout in the German-speaking Community were launched for. The BIPT coverage atlas shows what actually serves a given address.

Six situations, six answers

The row that misleads most people is the first one. A test run with the right method changes the diagnosis on its own in most cases.

How do you enforce your contract's minimum speed?

First, find the figure. At Proximus, it sits on the internet speed page by address; at Telenet, in the estimate provided when ordering; elsewhere, in the contract summary handed over before signing. Then build a file nobody can wave away with "it's your Wi-Fi":

• a computer plugged in over Ethernet directly into the modem, every other device disconnected;
• at least ten measurements over two weeks, several of them between 8pm and 11pm;
• the date, time and result of each test, download and upload;
• the contractual figure alongside, minimum speed and normally available speed;
• a written complaint, never just a phone call, with that table attached.

The EU Regulation classes a significant, continuous or regularly recurring gap as non-conformity. To our knowledge as of 26 September 2026, no Belgian tool produces automatic proof of that gap: your series of measurements, put to the provider, remains the key piece. Without a satisfactory reply, the Telecommunications Ombudsman Service steps in free of charge and can recommend compensation or termination without fees.

Before subscribing, compare offers on what they actually deliver to your address, not on their "up to". That is the logic behind our ranking of the best fiber internet offers in Belgium.

Definitions come from Regulation (EU) 2015/2120 and the BIPT decision of 2 May 2017; the legal floor, from the Royal Decree of 10 September 2023; GPON and XGS-PON capacities, from International Telecommunication Union recommendations. Provider pages consulted on 26 September 2026.