The plain-English, ACCC-grounded rundown of what actually slows an Australian NBN connection — and where to fix each cause.
NBN slowdowns almost always trace to one of six causes: evening peak-hour congestion (7–11pm), a plan speed tier lower than your household needs, in-home wiring faults, Wi-Fi limits between your device and the modem, an ageing modem, or your underlying connection technology (FTTP, FTTN, FTTC, HFC, Fixed Wireless or Satellite). The ACCC's Measuring Broadband Australia program reports that fixed-line typical evening (busy-hour) speeds sit close to advertised plan speeds on most retailers, so a large gap between what you measure and what you pay for is a signal worth investigating — not something to simply accept. Each cause below points to the page that fixes it.
Six causes account for most slow-NBN complaints in Australia. This hub names each one and points you to the page that handles it in depth — so you can go straight to the cause that matches your symptoms.
Speeds drop between 7pm and 11pm when your street shares network capacity. The ACCC measures this as the 'typical evening speed' for each plan.
Your line may be fine, but your plan (NBN 25, 50, 100+) is slower than your household needs. Measured speed near your tier's cap is normal, not a fault.
Old phone sockets, a poor connection point, or a modem several years old can cap speed well below what the line delivers.
Wi-Fi loses speed through walls and distance. A wired (Ethernet) test shows the true line speed; Wi-Fi shows what reaches your device.
The clearest way to separate congestion from a plan-tier problem is timing. Run a wired speed test at an off-peak hour (for example, 10am) and again during the 7–11pm evening window. If your off-peak speed is close to your plan's advertised rate but your evening speed drops sharply, that points to peak-hour congestion — the busy-hour effect the ACCC's Measuring Broadband Australia reports track quarter by quarter. If your speed is consistently well below the advertised rate at every hour, the issue is more likely your plan tier, your connection technology, or in-home hardware rather than network congestion. Testing wired rather than over Wi-Fi removes one big variable, because Wi-Fi loss between the modem and your device can mimic a slow line. Once you know which pattern you have, the fix path is different: congestion often needs a plan or provider change, while a flat under-delivery needs a benchmark check against what your tier should deliver.
A speed test gives you four numbers — download, upload, ping (latency) and jitter — but the number alone means nothing until you compare it to what your plan promises. A measured 40 Mbps download is underwhelming on an NBN 100 plan but perfectly normal on an NBN 50 plan. Latency (ping) matters most for video calls and gaming, while jitter — the variation in ping — explains why a call stutters even when the download figure looks fine. To read your own result properly, compare your evening download speed to your plan's advertised and ACCC-reported typical evening speed for that tier. If the gap is large and consistent, that is the evidence you need before contacting your retailer. The result-interpretation and benchmarking pages below walk through exactly how to make that comparison for your specific tier.
The rules on this page follow the official requirements published by ACCC Measuring Broadband Australia; NBN Co. Always confirm current rules and fees with the authority before you book.