nbn Speed Slower Than Plan? What to Check

If your nbn speed is slower than your plan, the first things to check are your Wi-Fi setup, the time of day, and the cabling inside your home—these account for most speed shortfalls. This guide walks through the practical checks and fixes you can do yourself before calling your provider, plus what to do if the problem is on the nbn network itself.

Formula

The calculator above works out your average download speed from a speed test. The formula is:

Speed (Mbps) = (Data downloaded in megabytes × 8) ÷ (Test duration in minutes × 60)

• Data downloaded – the amount of data transferred during the test, in megabytes (MB).
• Test duration – how long the test ran, in minutes.
• Speed – your average download speed, in megabits per second (Mbps).

Note the difference between megabytes (MB) and megabits (Mb): 1 byte = 8 bits. Internet plans are quoted in megabits per second, but file sizes are usually in megabytes. If you download a 300 MB file in 5 minutes, that’s 300 × 8 = 2400 megabits in 300 seconds, which is 8 Mbps.

Worked Example

Using the default values from the calculator: test duration = 5 minutes, data downloaded = 300 MB.

1. Convert megabytes to megabits: 300 MB × 8 = 2400 Mb.
2. Convert minutes to seconds: 5 min × 60 = 300 s.
3. Divide data by time: 2400 Mb ÷ 300 s = 8 Mbps.

So the average speed over that test is 8 Mbps. If your plan is 50 Mbps, this result is far below plan—time to investigate.

Why Your nbn Speed Might Be Lower Than Advertised

nbn plans are sold with a “typical evening speed� rather than a guaranteed maximum. The nbn Co. wholesale product has a maximum line rate, but your actual speed depends on your technology type (FTTP, FTTB, FTTN, HFC, FTTC), the distance from the node or exchange, and congestion on your provider’s network. Even on a 100 Mbps plan, you may see 80 Mbps at peak times—that’s normal. But if you’re getting 20 Mbps on a 100 Mbps plan, something is wrong.

Speed also varies by time of day. The nbn’s “typical evening speed� is measured between 7 pm and 11 pm, when networks are busiest. If you test at 3 am, you’ll likely see higher speeds. So always compare your speed test results to the plan’s evening speed, not the theoretical maximum.

Check Your Wi-Fi First

Wi-Fi is the most common culprit for slow nbn speeds. The nbn connection may be fine, but your Wi-Fi can bottleneck it. Here’s what to check:

• Distance and obstacles – Move closer to the router, or use a wired Ethernet connection for a definitive test. Walls, floors, and appliances weaken Wi-Fi.
• Band selection – Use the 5 GHz band if your router supports it; 2.4 GHz is slower but has better range. Many routers broadcast both, but your device may be stuck on 2.4 GHz.
• Interference – Other Wi-Fi networks, cordless phones, and microwaves can interfere. Change the Wi-Fi channel in your router settings.
• Old devices – Older phones or laptops may have slower Wi-Fi chips that cap your speed.

To isolate the issue, run a speed test on a device connected via Ethernet cable directly to your nbn modem/router. If that shows your full plan speed, the problem is Wi-Fi, not your nbn connection.

Test at the Right Time and Use the Right Server

Speed test results vary by server location. Use a server that’s geographically close to you, ideally the one your provider recommends. Also, test multiple times throughout the day—especially during the evening peak (7–11 pm) to see if you’re getting the “typical evening speed� promised on your plan. If you only test at off-peak times, you might see great speeds and miss a congestion issue.

Also, use a reliable speed test tool. Some free online tests are accurate, but others may be affected by your browser or device. For a fair test, close all other apps and tabs, and ensure no downloads or updates are running in the background.

Check Your nbn Connection Type and Cabling

Your nbn technology type affects your maximum possible speed. For example, Fibre to the Node (FTTN) and Fibre to the Building (FTTB) are more sensitive to distance from the node—the farther you are, the slower your line rate. Fibre to the Premises (FTTP) and HFC (cable) are generally more consistent.

Inside your home, check the cabling from the nbn connection point to your router. Old or damaged Ethernet cables, loose connections, or using a phone cable instead of Ethernet can cause speed drops. Also, if you have a separate modem and router, make sure they’re connected with a good quality Ethernet cable (Cat5e or better).

For FTTN/FTTB, the quality of the copper line from the node to your home matters. If you suspect a line fault, your provider can run a line test. They may also adjust your line profile to improve stability, but that can reduce speed if the line is noisy.

Check Your Plan and Provider’s Speed Claims

Not all plans are equal. Some providers offer “up to� speeds that are lower than the nbn wholesale speed. Check your plan’s “typical evening speed� (usually listed on the provider’s website or your bill). If you’re consistently below that, you may have a case for a complaint.

Also, check if you’re on a legacy plan that’s slower than current offerings. Sometimes providers change their speed tiers, and you might be on an old plan that’s no longer competitive. You can usually upgrade to a faster plan without changing your nbn technology.

If you’re on a 100 Mbps plan but your nbn technology only supports 50 Mbps (e.g., FTTN at a distance), you’ll never get 100 Mbps. Check your nbn technology and its maximum line rate—your provider can tell you.

When to Call Your Provider

If you’ve ruled out Wi-Fi, cabling, and time-of-day issues, and you’re still getting speeds far below your plan’s typical evening speed, contact your provider. Before calling, have your speed test results ready, including the date, time, and server used. Also, note whether the issue is consistent or intermittent.

Your provider can run a remote line test to check for faults. If the line is faulty, they may dispatch a technician. If the issue is congestion on their network, they may be able to move you to a less congested node or recommend a different plan.

If your provider doesn’t resolve the issue, you can escalate to the Telecommunications Industry Ombudsman (TIO) in Australia. They handle complaints about nbn speed issues that aren’t resolved by the provider.

Frequently Asked Questions

Why is my nbn speed slower at night?

Evening congestion is common. During peak hours (7–11 pm), more people are online, so providers’ networks can become congested. nbn plans advertise a “typical evening speed� that accounts for this. If your speed drops significantly during peak times but is fine at other times, it’s likely congestion. You can try a different provider that has more capacity, or upgrade to a plan with a higher speed tier.

Does my router affect my nbn speed?

Yes. An old or low-end router may not handle high-speed plans. Check if your router supports the speed of your plan (e.g., for 100 Mbps, you need a router with gigabit Ethernet ports and dual-band Wi-Fi). Also, router firmware updates can improve performance. If your router is more than 3–4 years old, consider upgrading.

What is a good nbn speed test result?

It depends on your plan. For a 50 Mbps plan, a good result is around 40–50 Mbps during off-peak, and at least 30 Mbps during evening peak. For a 100 Mbps plan, expect 80–100 Mbps off-peak and at least 60–70 Mbps in the evening. If you’re getting less than half your plan’s speed consistently, there’s a problem.

Can I speed up my nbn without changing plans?

Sometimes. Optimise your Wi-Fi (use Ethernet, move the router, change channels), update your router firmware, and check for background downloads. You can also ask your provider to check your line profile—if you have FTTN, they might adjust it to improve stability, but this can sometimes reduce speed. If your router is old, upgrading it can help.

Why is my upload speed slower than download?

That’s normal. nbn plans are asymmetric—they offer much faster download speeds than upload. For example, a 50/20 plan means 50 Mbps download and 20 Mbps upload. Your upload speed is also affected by the same factors as download, but it’s usually lower by design.

Is it worth upgrading to a higher nbn speed tier?

Only if you actually need it. If you’re on a 50 Mbps plan and only get 20 Mbps due to line distance or congestion, upgrading to 100 Mbps won’t help—you’ll still be limited by the same factors. First, fix the underlying issue. If you have FTTP or HFC and your Wi-Fi is good, upgrading can give you a real speed boost, especially if you have multiple users or stream 4K video.

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in t | Test duration | min | 5 | 1
in d | Data downloaded | MB | 300 | 1
out speed | Average speed | Mbps | (d * 8) / (t * 60) | 2