Why does my internet speed drop drastically during video calls?

[Ashurohilla]

Even with a 100 Mbps plan, my Zoom calls lag badly, especially in the evening. Speed tests look fine. Could this be packet loss or ISP throttling?

[Remu Leakey]

I’ve faced this same issue — blazing fast speeds on paper, but Zoom still lags like I’m on dial-up. After months of trial and error (and frustration), here’s what I figured out.

1. Your Speed Test Isn’t the Whole Story

Most speed tests (like Ookla or Fast.com) check download/upload under ideal conditions. But video calls don’t just rely on speed. They need stable, consistent connection — which is where things like latency, jitter, and packet loss come in. If any of those are off, Zoom will struggle even if your speed test shows 100 Mbps.

2. Evening Hours = Network Congestion

If your Zoom starts lagging every evening, you’re probably sharing bandwidth with a lot of neighbors. This is called peak hour congestion. ISPs often oversell their capacity, and when too many users stream, game, or call at the same time — speeds dip. And no, your 100 Mbps plan doesn’t guarantee 100 Mbps all the time.

3. ISP Throttling is Real (Even if They Deny It)

Some ISPs throttle or deprioritize certain services — like Zoom, Netflix, or gaming — during peak hours, especially if they detect heavy usage. They don’t always admit it, but forums are full of users catching them in the act. A VPN sometimes helps because it hides your traffic, but it’s not a fix-all.

4. Wi-Fi Weakness or Interference

Even if your main connection is solid, Wi-Fi can mess things up. Walls, microwaves, even your neighbor’s router can interfere with your signal. Try moving closer to your router, or better yet, connect via Ethernet. That alone fixed 70% of my call issues.

5. Background Apps & Devices

Check what else is using the network during your call. Smart TVs streaming, phones syncing photos, someone downloading games — all of it eats into your available bandwidth. Zoom doesn’t need a ton of speed, but it does need uninterrupted access.

6. Router Quality and Age

If you’re using the router your ISP gave you, it might not be handling traffic efficiently. A lot of those are entry-level devices. Upgrading to a better dual-band router with QoS (Quality of Service) features can make a huge difference — QoS lets you prioritize Zoom traffic so it gets the best share of your bandwidth.

7. Packet Loss: The Silent Killer

You mentioned packet loss, and yeah, that’s often the hidden problem. Even a tiny percentage of dropped packets can ruin a video call. It doesn’t always show up on speed tests. Try running a tool like PingPlotter to check your connection over time — it can reveal intermittent issues or bad routing.

What I Did That Actually Helped

• Switched from Wi-Fi to wired Ethernet

• Bought a mid-range router with QoS and prioritized Zoom

• Installed PingPlotter to monitor for packet loss

• Tested with and without VPN — noticed better performance in some cases with VPN on

• Called my ISP and asked for a line check — they found “signal noise” and replaced the outdoor cable

TL;DR:

Your internet may look fast, but Zoom needs consistency, not just speed. Packet loss, Wi-Fi interference, peak-time congestion, and ISP throttling are all very real. A few small changes — especially going wired and tweaking router settings — can make a massive difference.

Let me know if you want help reading your PingPlotter results or setting up QoS — I’ve been through this rabbit hole and am happy to help others avoid the headache.

[Author]

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