ISPs advertise maximum speeds under ideal conditions. Real-world speeds are typically 70–90% of the advertised figure even on a healthy connection. If you're seeing less than 50% of your plan speed, one of these eight causes is responsible. Run a speed test first to get your baseline, then work through this list.
1. Wi-Fi interference
Wi-Fi is almost always slower than a wired Ethernet connection. Interference from neighbouring networks, walls, and distance from the router all reduce throughput. Fix: Run your speed test via Ethernet cable. If wired is significantly faster, upgrade your router, add a mesh node, or switch from 2.4 GHz to 5 GHz band.
2. Router or modem bottleneck
Old routers cap throughput — a router made before 2019 may physically be unable to pass 500 Mbps. Fix: Check your router's maximum throughput spec against your plan speed. Many ISP-supplied routers are underpowered for modern gigabit plans.
3. Network congestion — peak hours
Most residential ISPs experience congestion between 7–11 PM when demand peaks. Fix: Run speed tests at different times of day. If results are consistently worse in evenings, contact your ISP — this is a known, addressable infrastructure issue.
4. ISP throttling
Some ISPs intentionally slow speeds to specific services (streaming, torrents) or after you exceed a data threshold. Fix: Use a VPN and rerun a speed test. If results improve significantly with the VPN, throttling is likely occurring. Document results with timestamps and contact your ISP or national regulator.
5. Too many active devices
Background processes — cloud sync (Dropbox, OneDrive), software updates, smart home devices — consume bandwidth silently. Fix: Check your router's connected device list. Pause or disconnect non-essential devices before your important speed test or video call.
6. Slow DNS server
Your DNS server affects how quickly domain names resolve — this makes your connection feel sluggish even when download speed is fine. Fix: Switch to Cloudflare DNS (1.1.1.1) or Google DNS (8.8.8.8) in your router settings. This takes two minutes and often noticeably improves perceived speed.
7. Old or faulty cables
A Cat5 cable caps at 100 Mbps. For gigabit speeds, you need Cat5e or better. Faulty connectors also degrade performance. Fix: Check that your Ethernet cables are Cat5e or Cat6, and try replacing them if wired speeds are lower than expected.
8. The speed test itself
Speed test results vary based on server location, server load, and time of day. A single result can mislead you. Fix: Run 3–5 tests at different times. SpeedCheckTest saves your last 8 results automatically — use this to spot patterns rather than reacting to a single data point. Read our guide on how to get the most accurate speed test result.
Sources: FCC Consumer Broadband Guide · OpenSignal State of Mobile Networks 2024 · BEREC Net Neutrality Guidelines