Why internet speed drops when a backup is running

Your video call gets choppy or web pages take longer to load as soon as a backup starts. The backup may be using most of your upload capacity, but Wi-Fi congestion or a busy computer can also be part of the problem.

Compare your connection before and during the backup to see what changes. The Speed Test measures download speed, upload speed, ping, and jitter. A second check can show whether the delay rises when your connection is busy.

Measure speed with the backup on and off

1. Open the Speed Test on the device that feels slow. Run it when the backup is paused or idle, and note the download speed, upload speed, ping, and jitter.
2. Start or resume the backup. Wait until it is actively transferring data, then run the Speed Test again on the same device. If possible, use the same connection and test server for both runs.
3. Compare the numbers. Look for a large drop in upload or download speed, or a rise in ping and jitter. Repeat the comparison once, since a single result can vary with other network activity.
4. If speed falls while the backup is active, run the Bufferbloat Test when it is safe to put the connection under load. It grades how much delay increases during downloading or uploading.

A speed test sends test traffic to its server, so it briefly uses your connection too. Avoid running it during a call or another time-sensitive task. If the backup is small or finishes quickly, wait until it is transferring steadily before testing.

What the result means

Upload speed drops, and other tasks feel slow

Many cloud backups send files from your computer to the internet. If the backup uses nearly all the available upload capacity, there may be little room left for video calls, messages, or page requests. Even downloads can feel slow because devices send small acknowledgments back to the server while receiving data. When the upload is crowded, those acknowledgments may wait in a queue.

Download and upload speed both drop on Wi-Fi

The backup may be using Wi-Fi airtime as well as internet capacity. Wi-Fi is shared radio time: devices take turns sending and receiving. A weak signal, interference, or several active devices can make each transfer take longer. Compare with a wired connection if you can.

Ping rises or the bufferbloat grade is low

When large transfers fill queues in a modem or router, small requests can wait behind them. This delay is called bufferbloat. The connection may still move a lot of data, but calls, games, and remote desktop sessions can feel sluggish. A poor grade points toward delay under load, not necessarily a low-speed internet plan.

Internet speed stays similar, but the computer feels slow

The backup might be reading many files, compressing them, or checking them for changes. That can use the computer's processor or storage even if the network is not full. A local backup to an external drive does not normally consume internet bandwidth, though a busy computer or USB connection can make other tasks slower.

Speed changes even when the backup is paused

The backup may not be the cause. Other devices, a changing Wi-Fi signal, or normal variation in the speed test can affect results. Repeat the comparison at a quiet time, and check whether the slowdown happens on another device too.

Reduce the slowdown

1. Limit the backup's upload rate. Look in the backup app's settings for a bandwidth or upload limit. If it offers one, start by leaving roughly 10 to 20 percent of the measured upload speed available for other tasks, then adjust based on how calls and browsing feel. App controls vary, and not every backup service has a limit.
2. Schedule large backups for a quieter time. Set them to run overnight or when nobody needs a call, game, or remote connection. If the backup app offers a schedule, use its own controls rather than repeatedly disconnecting the computer from the network.
3. Check whether Wi-Fi is involved. If possible, connect the computer to the router with Ethernet and repeat the comparison. On Windows 11, check the active network under Settings › Network & internet. On macOS, open System Settings › Network › Wi-Fi. If Ethernet performs better, move closer to the router or try a less crowded Wi-Fi band if your router and device support one.
4. Give calls and other important traffic room. Pause the backup during a call, or reduce its upload limit. Some routers offer traffic prioritization or smart queue management, which can help keep interactive tasks responsive while a transfer runs. Router features and names differ, so check the controls for your model.
5. Check for a computer bottleneck. Pause the backup briefly and see whether the computer becomes responsive. On Windows, open Task Manager with Ctrl + Shift + Esc and check processor, disk, and network activity. On macOS, open Activity Monitor from Applications › Utilities and inspect its CPU, Disk, and Network views.
6. Repeat the test under consistent conditions. Use the same device and connection, avoid other large transfers, and compare a few runs. If speed remains low with the backup stopped, troubleshoot the connection separately rather than assuming the backup is responsible.

Tell a backup problem from an internet problem

If pausing the backup quickly restores speed, the backup is likely competing for bandwidth or computer resources. If the problem continues, test another device on the same network. When all devices are slow, check the router and internet connection. When only one computer struggles, look at its Wi-Fi link, background transfers, processor, and storage.

The Speed Test measures connection performance, not the speed of the backup provider or the time needed to scan your files. TooLab's Speed Test exchanges test data with its server; your backup files are not part of that test.