Everything you do online is chopped into small chunks called packets, fired across the network, and reassembled at the far end. Packet loss is exactly what it sounds like: some of those chunks never arrive. The internet was designed to tolerate this — which is precisely why packet loss is so sneaky. Your downloads look fine while your games and calls quietly fall apart.
Why downloads hide it but games can't
Most traffic — web pages, file downloads, Netflix buffering ahead — rides on TCP, a protocol that checks every packet arrived and automatically re-sends anything missing. Lose a packet and TCP retransmits it; you never notice beyond a slightly slower transfer. (Heavy loss does still hurt: TCP interprets it as congestion and throttles itself, so a lossy line tests slower than it should.)
Real-time traffic can't play that game. A video call or a Valorant tick is only useful right now — by the time a lost packet could be re-sent, the moment it described has passed. So games and calls mostly use UDP, which doesn't retransmit, and they simply have to cope with the gaps: rubber-banding and teleporting players in games, robotic audio and frozen frames in calls. That's why a connection can feel “fast but broken” — the speed test number is fine while the real-time experience is awful.
What counts as acceptable?
- 0% — the goal, and what a healthy wired connection should show.
- Under ~0.5% — generally unnoticeable in everyday use.
- ~1% — downloads still look normal, but competitive games stutter and calls start to artefact. Worth fixing.
- 2–5%+ — calls degrade badly, games become unplayable, and even browsing starts to feel sticky. Something is genuinely wrong.
Common causes, roughly in order of likelihood
- Wi-Fi interference and weak signal — by far the most common source in homes. Radio retransmissions mask mild loss but give up under heavy interference. Distance, thick walls and congested channels all contribute; our router placement guide fixes a lot of this.
- Damaged or loose cables — a kinked Ethernet lead, a chewed cable behind the desk, corroded coax connectors outside the house. Cheap to check, frequently guilty.
- Overloaded router or modem — ageing hardware running hot, or a router buckling under dozens of devices, starts silently dropping packets. A reboot helping for a day is the classic symptom.
- A saturated connection — when uplink or downlink is completely full, queues overflow and packets are dropped. If loss appears only while someone backs up to the cloud, this is your culprit.
- ISP network congestion or line faults — peak-hour loss on cable segments, water in street cabinets, faulty ports. The giveaway is loss that persists on a wired connection and follows a time-of-day pattern.
Step-by-step diagnosis
- Measure first. Run a NetStartr test — packet loss is reported alongside ping and jitter. One test is a snapshot; run three.
- Go wired and re-test. If loss disappears on Ethernet, the problem is your Wi-Fi — signal, channel or interference — not your line.
- Swap the cable. If you're already wired, try a different Ethernet lead and port. Seriously — this fixes more cases than anyone expects.
- Reboot and unburden the router. Power-cycle modem and router, pause cloud syncs and big downloads, then re-test. Loss that vanishes on a quiet line points to saturation, not faults.
- Test at different times. Loss at 9 PM but not 9 AM suggests neighbourhood congestion — an ISP problem, not a you problem.
- Build evidence and call. Persistent loss on a wired, quiet connection is squarely your ISP's to fix. Timestamped results across several days make the support call short; our guide to proving your speed to your ISP covers the script.
Packet loss is the most under-diagnosed connection problem precisely because the headline speed number can look perfect throughout. Measure it directly, halve the problem space with one Ethernet cable, and you'll usually have your answer within ten minutes.