Why is my NBN so slow?

Slow NBN is one of the most common complaints we hear from clients across Melbourne and the Mornington Peninsula. The frustrating reality is that “slow NBN” can mean half a dozen different things — and the fix for each one is completely different.

This guide walks you through every major cause, in order of how to diagnose them. Start with Step Zero below — it will tell you which section is most relevant to your situation before you read any further.

If you’ve already tried everything and still have issues, we’re happy to help — call us on 0484 357 559 or book a technician here.

Step Zero: Run a Speed Test First

Before reading through the causes below, take three minutes to run a proper speed test. This single step tells you whether you have an NBN problem, a Wi-Fi problem, or a device problem — and points you to the right section.

How to run a diagnostically useful speed test:

1. Connect your laptop or desktop directly to your modem via an ethernet cable — not Wi-Fi
2. Close all other applications and browser tabs on the device you are testing from
3. Go to fast.com or speedtest.net and run the test
4. Note your download speed result
5. Unplug the ethernet cable and repeat the test over Wi-Fi from the same room as your modem
6. Run both tests again in the evening between 7pm and 11pm and note any difference from your daytime result

Don’t know what speed your plan should deliver?
Log into your ISP account portal, check your welcome email, or call your ISP and ask for your plan’s advertised download speed and “typical evening speed.” ISPs are required by the ACCC to provide this figure — it is not optional information.

Reading your results:

If your wired speed is significantly below your plan speed at any time of day, you have a documented, actionable fault. Keep screenshots of your speed test results — you will need them if you contact your ISP or escalate to the TIO.

1. ISP Network Congestion and Traffic Management (CVC Throttling)

The most common cause of slow NBN — especially in the evenings — is not a problem with your personal connection. It is a problem with your ISP’s network capacity.

How NBN wholesale capacity works:
NBN Co sells wholesale network access to Retail Service Providers (RSPs) such as Telstra, Optus, and TPG through a mechanism called a Connectivity Virtual Circuit (CVC). Each CVC has a bandwidth limit. When an ISP has not purchased enough CVC capacity to serve all their customers simultaneously — which is common during peak hours between 6pm and 11pm — speeds slow down for everyone on that provider’s network in your region simultaneously.

This is not targeted at your account or anything you are accessing. It affects all users on an under-provisioned RSP network in your area at the same time.

ISPs may also apply traffic management policies to specific types of traffic — such as peer-to-peer file sharing — under their published Fair Use Policy. This is separate from CVC congestion and is based on your plan’s terms. You can find your ISP’s Fair Use Policy on their website or by asking their support team directly.

How to tell if CVC congestion is your problem:

• Speeds are noticeably worse in the evenings (6–11pm) but normal during the day or at weekends
• Running the wired speed test from Step Zero shows evening results well below your plan’s “typical evening speed” figure
• The slowdown affects all devices in your home simultaneously

What to do:

1. Run speed tests at different times of day over 3–5 days and keep a record (date, time, result)
2. Compare your evening speed results to your ISP’s published “typical evening speed” for your specific plan
3. If your recorded speeds are consistently below that published figure, contact your ISP formally and request a resolution — ask for a fault reference number
4. If your ISP cannot resolve the issue within a reasonable timeframe, you have legal rights — see the Know Your Rights section below
5. The ACCC’s Measuring Broadband Australia report publishes comparative performance data for major Australian RSPs — use it to evaluate whether switching providers would help before signing a new contract

2. Wi-Fi Band and Router Placement

An often-overlooked cause of slow speeds is the frequency band your router is using. Most modern routers broadcast on two bands: 2.4 GHz and 5 GHz, and connecting to the wrong one for your situation can significantly affect performance.

2.4 GHz: Better range and wall penetration, but more crowded — it shares spectrum with microwaves, cordless phones, and neighbouring Wi-Fi networks. Maximum real-world speed is typically 50–150 Mbps.

5 GHz: Much faster with less interference, but shorter range — the signal weakens more quickly the further you are from the router or through walls.

Router placement also matters significantly. A router tucked inside a cupboard, behind a TV unit, or in a corner of the house will deliver noticeably worse Wi-Fi coverage than one positioned centrally and elevated, away from other electronics.

What to do:

• If you are close to your router, connect to the 5 GHz band for maximum speed
• If you are in another room or on a different floor, try both bands and compare your speed test results
• If your router only broadcasts a single network name (SSID), check whether your router’s admin interface allows you to separate the 2.4 GHz and 5 GHz bands for manual selection

For a detailed breakdown of which band is best for different environments, see our guide on the difference between 2.4 GHz and 5 GHz Wi-Fi.

3. NBN Installation Issues

If your speeds have been consistently slow since the day your NBN was first connected — not just at peak hours, and not varying by device — the original installation may be the cause.

Symptoms that point to an installation issue:

• Slow speeds from day one of service, with no variation by time of day
• Your wired speed test (Step Zero) is slow even when directly connected to the modem
• You moved into a property and inherited an existing NBN connection you did not set up yourself
• You performed a self-install and are unsure whether all steps were completed correctly

Common installation-related causes:

• Incorrect or damaged internal cabling — particularly relevant for FTTP and HFC connections
• Missing, damaged, or incorrectly fitted faceplate or splitter on the telephone wall socket — relevant for FTTN and FTTB connections
• Faulty NTD (Network Termination Device) — the NBN wall box your modem plugs into
• Modem connected to the wrong port on the NTD, or not configured with your ISP’s correct settings
• Poor-quality or incorrect-length patch cable between the NTD and modem

Who is responsible and what to do:

If you are renting and suspect the in-home cabling is causing the issue, your landlord may be responsible for maintaining fixed premises infrastructure. Check your tenancy agreement and contact your state’s consumer affairs body if you are unsure of your entitlements.

4. Network Congestion — Multiple Devices and Peak Hours

Even when your NBN connection is performing well, having multiple devices active simultaneously places increased demand on your available bandwidth.

Two distinct types of congestion can affect your speeds:

In-home congestion: Multiple devices streaming, gaming, or downloading at the same time will divide your available bandwidth between them. A household on an NBN 50 plan with four people simultaneously streaming 4K video (which requires approximately 25 Mbps per stream) will experience slowdowns regardless of connection quality.

ISP peak-hour congestion: When too many users in your area are online simultaneously, your ISP’s network becomes overloaded if they have not provisioned sufficient CVC capacity. This is the more common cause of peak-hour slowdowns and is covered in detail in Section 1 above.

How to tell which type you have:

• Slowdowns only when multiple devices are active simultaneously → likely in-home congestion
• Slowdowns in the evening even on a single device → likely ISP peak-hour congestion (see Section 1)

What to do for in-home congestion:

• Identify which devices or applications are consuming the most bandwidth — most modern routers show per-device usage in the admin interface
• Schedule large downloads (software updates, backups, game downloads) for overnight when usage is lower
• Consider upgrading to a higher NBN speed tier if your household’s simultaneous usage regularly exceeds your plan capacity
• Quality of Service (QoS) settings on modern routers allow you to prioritise specific devices or applications — useful if one person’s video calls are being disrupted by another device’s background downloads

5. Distance From the Node (FTTN Connections)

If you are on a Fibre to the Node (FTTN) NBN connection, your speed is significantly affected by the physical distance between your home and the nearest NBN node — and by the quality of the copper telephone wiring that runs that distance.

FTTN uses fibre optic cable from the exchange to a street-side node cabinet, then relies on the existing copper telephone network to carry the connection from the node to your home. Copper degrades over distance — the signal quality and maximum achievable speed decrease the further the signal has to travel.

• Homes within 200–400 metres of the node typically achieve speeds close to the plan maximum
• Homes 500–800 metres from the node will experience noticeably reduced speeds
• Homes more than 800 metres from the node may find that even a top-tier plan cannot deliver significantly better performance than a lower-tier one

What to do:

• Check your connection type at nbn.com.au — not all NBN connections are FTTN
• If you are on FTTN and experiencing consistently poor speeds, contact your ISP to request a line test — they can measure your actual copper line quality and advise on the maximum achievable speed at your address
• If NBN Co has determined that your line cannot deliver your current plan’s speeds, you have rights — see the Know Your Rights section immediately below
• In some areas, NBN Co is progressively upgrading FTTN connections to FTTP (Fibre to the Premises) — check nbn.com.au/upgrades for your address eligibility

⚖️ Know Your Rights: When Your ISP Can’t Deliver What You’re Paying For

If your NBN speed is consistently below what your ISP advertises — for any reason — you are not stuck. Australian consumer law and ACCC telecommunications regulations give you specific, enforceable rights.

Your entitlements:

1. The right to see your plan’s “typical evening speed”
ISPs are required by the ACCC to publish “typical evening speed” figures for every NBN plan they sell. This is the speed you should typically receive between 7pm and 11pm. If your ISP does not display this figure, ask them directly in writing — they are obligated to provide it.

2. The right to move to a lower-cost plan without exit fees
If your ISP consistently cannot deliver your plan’s advertised speeds and cannot resolve the issue after a formal complaint, you are entitled to move to a lower-cost speed tier without paying any cancellation or plan-change fee. This is not a favour your ISP grants you — it is a consumer protection.

3. The right to exit your contract
If the speed shortfall is material and ongoing, and your ISP cannot fix it within a reasonable timeframe, you may be entitled to exit your contract entirely without paying an early termination fee. Contact your ISP in writing (email creates a documented record) and state the issue clearly, referencing your speed test logs.

4. The right to escalate to the TIO
If your ISP does not resolve your complaint within a reasonable timeframe — typically 15 business days — you can escalate for free to the Telecommunications Industry Ombudsman (TIO): Australia’s independent telecommunications dispute resolution body. It is free to use and requires no legal representation.

📎 Lodge a complaint: tio.com.au

How to build a strong complaint case:

• Log speed test results over at least 5 days (date, time, wired result, Wi-Fi result, test tool used)
• Save copies of all communications with your ISP in writing
• Record your plan name, advertised speed, and the “typical evening speed” figure from your plan documentation
• Ask for a formal fault reference number when you lodge your complaint with your ISP — this creates an accountable record

Compare RSP performance before switching providers:
The ACCC’s Measuring Broadband Australia report publishes comparative performance data for major RSPs — it is the most authoritative guide to which providers actually deliver their advertised speeds in Australia.

6. You May Be on the Wrong Speed Tier

One of the most common sources of slow NBN complaints is simply being on a lower speed tier than expected — or not knowing what speed your plan is actually supposed to deliver.

NBN speed tiers in Australia (2026):

Typical evening speeds are indicative — actual performance varies by ISP, location, and CVC provisioning.

What to do:
Log into your ISP account portal, check your current plan speed, and compare it to your Step Zero speed test result. If you are receiving speeds close to your plan’s typical evening speed, you are not experiencing a fault — you may simply need to upgrade your plan tier to match your household’s usage needs.

If your actual speed is significantly below your plan’s typical evening speed, follow the complaint pathway in the Know Your Rights section above.

7. Your Modem or Router May Be the Bottleneck

Even with a fast NBN connection, an older or under-specced modem or router can prevent you from receiving full speeds — and the NBN connection itself will appear to be the problem when it is not.

Common hardware bottlenecks:

Older Wi-Fi standards: A router that only supports 802.11n (Wi-Fi 4) has a real-world maximum of approximately 70–150 Mbps — which will cap your speeds on any NBN plan above 100 Mbps regardless of your connection quality. Wi-Fi 5 (802.11ac) supports up to ~600 Mbps real-world. Wi-Fi 6 (802.11ax) is recommended for NBN 250 and above.

Slow ethernet ports: Some older routers and modems have Fast Ethernet ports with a hard maximum of 100 Mbps. If your device has Fast Ethernet ports (not Gigabit), no NBN plan above 100 Mbps can deliver more than that figure via a wired connection. Check your modem’s specifications — Gigabit Ethernet ports are required for NBN 250 and above.

ISP-supplied modem limitations: Entry-level modems bundled with some ISP plans are not always capable of delivering NBN 250 or NBN 1000 speeds. If you upgraded your NBN plan recently and speeds did not improve, your modem’s capability ceiling may be the reason.

How to check your router’s specifications:
Find your router’s model number (usually on the label on the bottom or back of the device), then search “[router model] specifications” to confirm its Wi-Fi standard and ethernet port type.

What to do:
If you are on NBN 100 or above and your router or modem is more than 5 years old, a hardware upgrade is likely to be the fastest and most cost-effective performance improvement available to you — often before any ISP involvement is needed.

8. Test Wired vs Wireless to Isolate the Problem

If you have not yet run the wired speed test from Step Zero, do this before anything else. It is the single most important diagnostic step for slow NBN.

Wi-Fi speeds are affected by distance from the router, building materials, interference from other devices and neighbouring networks, and the number of devices connected simultaneously. These factors have nothing to do with your NBN plan or connection quality.

The diagnostic test:
Connect a laptop directly to your modem with an ethernet cable and run a speed test at fast.com or speedtest.net. Then disconnect and repeat the test over Wi-Fi from the same location.

Interpreting the result:

• Wired speed close to plan speed, Wi-Fi much slower → Your NBN connection is performing correctly. The issue is in your home Wi-Fi network. See Section 2 (Wi-Fi Band and Router Placement).
• Both wired and Wi-Fi speeds slow → The issue is with the NBN connection or ISP, not your Wi-Fi. See Sections 1, 3, 5, and the Know Your Rights section.
• Wired speed slow only in the evenings → Peak-hour CVC congestion at your ISP. See Section 1 and the Know Your Rights section.

9. Virus or Malware Consuming Your Bandwidth

If you have worked through all the sections above and your connection is still slow, a malware infection could be using your internet connection in the background without your knowledge. Certain types of malware — including adware, spyware, and cryptomining software — run silently and can consume significant bandwidth.

How to check whether malware is using your bandwidth:

Step 1 — Check per-process network usage in Task Manager
Open Task Manager (Ctrl+Shift+Esc) and click the Network column header to sort all running processes by their current network usage. Any process consuming significant bandwidth that you do not recognise by name is worth investigating — right-click it and select “Open file location” to see where the executable is stored. Legitimate Windows system processes run from C:\Windows\System32. Processes running from unusual locations such as AppData folders, Temp directories, or random folders outside of Program Files should be treated with suspicion.

Step 2 — Check your router’s connected device list
Log into your router’s admin interface (usually accessible at 192.168.0.1 or 192.168.1.1 — check the label on your router for the address and login details). Look for the connected devices list and, if available, per-device bandwidth usage. An unknown device on your network consuming data may indicate an unauthorised connection rather than local malware.

Step 3 — Run a dedicated malware scan
Windows Defender provides baseline protection, but for a thorough second-opinion scan we recommend downloading and running Malwarebytes Free — available directly from malwarebytes.com only. It specifically detects cryptomining malware, adware, and browser-based exploits that standard antivirus tools sometimes miss. Download it from the official site only.

Step 4 — Audit your browser extensions
Browser-based cryptomining via malicious extensions is a common attack vector. In Chrome, go to Settings → Extensions and remove any extension you do not recognise or did not deliberately install. In Edge, go to Settings → Extensions. Malicious extensions commonly disguise themselves as PDF tools, ad blockers, or video download helpers.

If you are not comfortable performing these steps, or if a scan returns results you are unsure how to interpret, contact our team — we offer both remote and in-home support across Melbourne and the Mornington Peninsula.

Frequently Asked Questions

Why does my NBN keep dropping out even when the speed seems fine?
Slow speeds and dropouts are different problems with different causes. A stable but slow connection is typically a congestion or hardware issue. A connection that drops entirely — even when speeds seem adequate at other times — more commonly points to a modem fault, line instability, or interference at the exchange or node level. See our step-by-step guide on what to do if your NBN keeps dropping out for a dedicated walkthrough.

Why is my NBN so slow at night?
Evening slowdowns are almost always caused by peak-hour CVC congestion at your ISP’s network — when too many users are online simultaneously and your ISP has not provisioned enough wholesale capacity to serve them all at full speed. This is particularly common with budget ISPs. Running a speed test during the day and comparing it to an evening test will confirm this pattern. If the gap is significant and consistent, you are entitled to take action — see the Know Your Rights section above.

Can a faulty modem or router cause slow NBN speeds?
Yes — and it is one of the most commonly overlooked causes. An outdated modem or router that does not support your plan’s maximum speed will bottleneck your connection even when the NBN side is performing perfectly. Regular firmware updates can help, but if your hardware is more than 4–5 years old and you are on NBN 100 or above, an upgrade is likely the most effective fix. See Section 7 above for detail on what to check.

Will switching NBN providers improve my speed?
Sometimes. If your current ISP has consistently poor peak-hour performance, switching to a provider with better CVC provisioning can make a material difference. The ACCC’s Measuring Broadband Australia report compares major RSP performance and is the best independent guide to which providers reliably deliver advertised speeds in Australia. Check it before committing to a new contract.

What should I do if my ISP says there is nothing wrong but my speeds are still slow?
Document your speed test results over at least five days — morning, afternoon, and evening — and present them to your ISP in writing. If your recorded speeds are consistently below your plan’s published “typical evening speed,” you have a documented case. If your ISP does not resolve it within a reasonable timeframe, escalate to the Telecommunications Industry Ombudsman (TIO) at tio.com.au — it is free and does not require a lawyer.

Still Having Issues? We Can Help.

If you’ve worked through this guide and your NBN is still not performing the way it should, it may be time for a professional diagnosis. At Computer Technicians, we troubleshoot NBN, Wi-Fi, and networking issues for homes and businesses across Melbourne and the Mornington Peninsula — with honest advice on whether the fix is a setting change, a hardware upgrade, or an ISP complaint.

📞 Call 0484 357 559 or book a technician online for an upfront assessment today.