Not Getting Advertised Internet Speed: How to Fix It

Step 1: Test correctly with a wired connection

To isolate whether your ISP is delivering the advertised speed, test under controlled conditions: connect your computer directly to the modem via Ethernet cable (bypass the router entirely), run a speed test at speedtest.net, and do so during off-peak hours before 6 PM on a weekday. Wi-Fi overhead, router processing, and peak-hour congestion all reduce speeds independently of what the ISP delivers.

Step 2: If wired modem speed is near advertised, the gap is in your network

If your direct-to-modem wired speed test is within 80–90% of your plan speed, the ISP is delivering correctly. The gap you experience on devices is caused by Wi-Fi signal quality, router processing overhead, or old Ethernet cables. Upgrading your router or switching to a 5 GHz Wi-Fi band will close this gap without involving the ISP.

Step 3: Check modem signal levels

If wired modem speed is well below advertised, access the modem's signal diagnostics at 192.168.100.1 (most cable modems). Check downstream power levels — they should be between -7 and +7 dBmV. Check SNR (signal-to-noise ratio) — it should be above 30 dB. Values outside these ranges indicate a line quality problem between your home and the ISP node, which requires a technician visit.

Step 4: Check for a modem bottleneck

A DOCSIS 3.0 modem is physically incapable of delivering gigabit speeds regardless of your plan. Check your modem model and its DOCSIS version — DOCSIS 3.1 is required for gigabit cable plans. If your ISP upgraded your plan but your modem is old hardware, the modem is the bottleneck. Contact your ISP about a modem upgrade or purchase a DOCSIS 3.1 modem.

Step 5: Document slow speeds with timestamped screenshots

To build a case with your ISP, run speed tests at different times of day over 7 or more days and screenshot each result — most speed test tools include timestamps automatically. Note the date, time, and result. Patterns such as slow speeds only during evening hours indicate peak-time congestion at the ISP node, which is a legitimate service quality complaint.

Step 6: Call ISP and reference documented tests

Contact your ISP's technical support line and provide the documented speed test results with dates and times. Request a line check and technician visit. ISPs are generally responsive when presented with specific timestamped data rather than vague complaints. Ask them to check signal levels at the node and the line running to your home.

Step 7: File FCC complaint if speeds remain below 80% for 30+ days

If speeds consistently remain below 80% of your advertised plan speed for more than 30 days without resolution, file a complaint with the FCC at consumercomplaints.fcc.gov. ISPs are required to respond to FCC complaints within 30 days. Include your documented speed tests, ISP case numbers, and dates of contact. State public utility commissions are an additional avenue for complaints.

Frequently Asked Questions

Is advertised internet speed guaranteed?

No. ISP advertised speeds are marketed as "up to" maximums, not guarantees. Most ISP service agreements specify that speeds are best-effort and may vary based on network conditions, your equipment, and the number of simultaneous users. However, consistently receiving less than 80% of the advertised speed — especially on a wired connection directly to the modem — is grounds for a legitimate service complaint.

How much slower than advertised is acceptable?

The FCC's Measuring Broadband America reports have historically used 80% of advertised speed as the threshold for adequate service. Getting 800 Mbps on a 1 Gbps plan is normal. Getting 400 Mbps consistently — especially at non-peak hours on a wired connection — is not. Wi-Fi connections are excluded from this benchmark since Wi-Fi performance depends on your own equipment and environment.

How do I complain about slow internet speed?

Start by calling your ISP with documented timestamped speed test results and requesting a line check. If that does not resolve the issue within two to four weeks, file a complaint with the FCC at consumercomplaints.fcc.gov — ISPs must respond within 30 days. You can also contact your state's public utilities commission. For egregious cases, the Better Business Bureau and state attorney general's consumer protection office are additional options.