Why do my video calls stutter when the speed test says everything is fine?
Speed is not the only number and it is rarely the one that breaks a call. What latency, jitter and packet loss actually are, how to measure them at home, and which one your symptom points to.
- Difficulty
- intermediate
- Time
- 15 min
- Read
- 4 min
Short answer
Speed measures how much data arrives per second. Latency measures how long each piece takes to get there, jitter measures how much that delay varies, and packet loss measures how much never arrives. Calls, games and video conferencing are ruined by jitter and loss while being perfectly happy on a modest speed — which is why a 500 Mbps connection can still stutter.
A speed test answers one question well and three others not at all. It is a bulk transfer measurement: it pours data as fast as it can for a few seconds and reports the rate. Real-time traffic behaves completely differently. A call sends small pieces continuously and needs each one to arrive on time, in order. If they arrive in bursts, or some do not arrive, the call breaks up even though the total volume of data would fit down the line a hundred times over.
Step by step
- Learn the four numbers and what each governs.Speed governs how long a download takes. Latency, quoted in milliseconds and often called ping, governs how responsive everything feels. Jitter is the variation in latency and governs whether real-time audio holds together. Packet loss is data that never arrives and governs the dropouts and frozen frames.
- Run a test that reports all four.Most speed test sites now report latency and jitter alongside the speeds, and several offer a loaded latency or bufferbloat test. That last one is the important one, because it measures latency while the line is busy rather than while it is idle.
- Pay particular attention to latency under load.A connection with 12 ms idle latency that climbs to 400 ms while something downloads has bufferbloat, and that is exactly what makes calls fall apart the moment anyone else in the house does anything.
- Test on ethernet first, then on wifi in the same spot.This separates the line from the wifi. Wifi adds jitter of its own, particularly on a congested 2.4 GHz band or at the edge of coverage, and a big difference between the two tests points squarely at the wireless link.
- Fix bufferbloat with smart queue management if your router has it.Many modern routers offer smart queue management, adaptive QoS or an anti-bufferbloat setting. Enabling it and telling it your actual line speeds keeps latency low while the line is busy, at the cost of a small amount of peak throughput. It is the single most effective change for a household where calls break when someone starts a download.
- Reduce jitter at the wifi end.Move the working device to 5 GHz, closer to a node, or onto a cable. Jitter caused by a marginal wireless link cannot be fixed by any amount of extra broadband speed.
- Record what you find before you complain.If the line itself shows loss or high latency at particular times of day, keep dated results from an ethernet-connected device. That is the evidence a provider will act on; a report of it feels slow is not.
If it doesn't work
Calls are fine alone, terrible when others are at home
Cause: Bufferbloat, or a saturated upload — Fix: Enable smart queue management, and check nothing is uploading continuously. Both fixes matter and they address different halves of the problem.
Audio robotic, video freezing in short bursts
Cause: Packet loss — Fix: Test wired. If loss disappears, it is the wifi. If it persists, report it to the provider with the test results — loss on the line is a fault, not a capacity issue.
Everything feels sluggish to respond, but downloads are fast
Cause: High baseline latency — Fix: Some connection technologies have inherently higher latency, notably satellite and some mobile broadband. If it is a fixed line and latency is consistently high when idle, that is worth reporting.
Only bad in the evening
Cause: Contention — the shared part of the network is busy — Fix: Test at several times and record the pattern. Consistent evening degradation across a whole area is a provider capacity problem and is worth reporting with the timings.
Questions people ask
What is a good ping for a UK connection?
On a fixed line, low tens of milliseconds to a UK server is normal and good. What matters more than the absolute figure is that it stays roughly the same when the connection is busy.
Will upgrading to a faster package fix stuttering calls?
Usually not. If the speed test already shows far more than the call needs, adding more speed changes nothing. Latency, jitter and loss are separate properties and a bigger package does not necessarily improve any of them.
Is jitter a wifi problem or a broadband problem?
It can be either, which is why the wired-versus-wireless test is the one to run first. Wifi is the more common source in a home.