Why enabling QoS can reduce peak throughput

You turn on QoS to stop downloads from disrupting calls, then notice your speed test no longer reaches its old peak. This can be normal: some QoS settings deliberately hold back traffic so the router can manage queues and reduce delay.

QoS means quality of service. The Bufferbloat Test can help you check whether the lower speed comes with a useful improvement in delay under load, or whether a setting is simply limiting your connection too much.

Compare QoS on and off

1. Open the Bufferbloat Test and run it with your current router settings. Note the grade and the delay while the connection is busy.
2. Repeat the test when no one else is streaming, gaming, downloading, or making a call. Keep the same device and connection type for each run.
3. If you can, connect the computer to the router with Ethernet. If you use Wi-Fi, stay in the same place and use the same band for every test.
4. Turn QoS off in the router settings, then run the test again and note the result. Restore your original setting before changing anything else.
5. Compare the results. Look at both the grade and how much the delay rises during a download or upload, not just the highest speed number.

For a fair comparison, test at a similar time of day and make only one router change at a time. A busy household or a changing connection to your provider can affect the results.

What the result means

Speed is lower, but delay under load improves

QoS is likely shaping traffic, which means it is controlling how quickly data enters the router's queue. A lower peak can be a worthwhile trade if calls, games, or remote work are more responsive while other devices use the internet. The right setting depends on which matters more in your home.

Speed is lower and the delay grade does not improve

The QoS rate limit may be too low, or the router may be using a method that does not manage busy queues well. A lower peak without a noticeable reduction in loaded delay suggests the setting is not giving you much in return.

Speed is similar with QoS on and off

Your router may prioritize certain traffic without applying a strict overall cap, or the test may not have filled the connection enough to reveal a limit. QoS settings differ by router, so check whether yours offers bandwidth limits, device priorities, or a queue-management option.

Results change widely between runs

That does not automatically point to QoS. Wi-Fi interference, other household traffic, or a fluctuating provider connection can change the result. Repeat the comparison under steadier conditions before adjusting your router again.

How to tune QoS without guessing

1. Confirm the connection you are testing. Use the same computer and wired or wireless connection each time. In Windows 11, check Settings › Network & internet. On macOS, check System Settings › Network. A phone on cellular data is not testing your router's QoS.
2. Check whether QoS has a bandwidth cap. Open your router's settings and look for QoS, traffic management, bandwidth control, or smart queue management. Names and menu locations vary. Some settings assign priority only, while others require download and upload limits.
3. Use a realistic rate if the router asks for one. Set the limits below the connection's stable real-world speeds, not above the maximum listed in your internet plan. A starting point around 90 percent of a steady measured rate can help, but the best value depends on your connection and router. Test again and adjust in small steps.
4. Prioritize the traffic that matters. If you only need calls to stay clear, prioritize the device or traffic category used for calls instead of applying a very low cap to every device. A high-priority setting cannot create extra internet capacity when the connection is saturated.
5. Retest after each change. Save one change, then repeat the Bufferbloat Test under the same conditions. Keep the setting only if it improves loaded delay enough to justify any loss in peak speed.
6. Check the router's limits. If speeds stay much lower with QoS enabled even after you raise its limits, the router may not have enough processing capacity to handle that feature at your internet speed. Check for a firmware update or compare results with QoS off.

Why QoS can lower the speed test peak

When several devices send data at once, packets can build up in a queue inside the router. That queue adds delay, sometimes called bufferbloat. QoS can manage the queue by scheduling traffic or limiting how quickly data is sent into it. If the router allows traffic to fill the connection completely, it may have less control over that queue.

Some routers therefore set a ceiling below the maximum connection rate. That gives the router room to manage traffic, but it also means a speed test may show a lower peak by design. Other routers use priority rules without a broad cap, so enabling QoS does not always reduce throughput.

QoS cannot make your internet plan faster or add capacity to the provider's network. Its purpose is to decide how available capacity is shared, especially when several devices compete for it.