Packet Loss: What It Is, What Causes It, and How to Fix It
Packet loss is the silent killer of real-time communication. Unlike high ping — which at least gets your data to its destination, just slowly — packet loss means your data never arrives at all. Even 1% packet loss is enough to make voice calls sound broken, games feel unresponsive, and video calls freeze. Here's everything you need to know to diagnose and fix it.
Packet loss occurs when data packets fail to reach their destination. It's measured as a percentage of sent packets that never arrive. 0% is the target — even 0.5% causes noticeable issues in real-time applications. The most common causes are Wi-Fi interference, faulty cables, congested routers, and ISP network problems.
What Is Packet Loss?
Every piece of data you send or receive over the internet is broken into small chunks called packets. A video call, a game state update, a web page download — all of these are transmitted as streams of individual packets, each tagged with destination information and a sequence number so the receiving end can reassemble them in order.
Packet loss happens when one or more of these packets fails to reach the destination. The packet is simply gone — dropped somewhere along the network path between your device and the server. The receiving application gets a gap in the data stream.
How badly this matters depends entirely on the application:
- Streaming video / file downloads — TCP (the protocol used by HTTP) automatically detects and retransmits lost packets. The download takes slightly longer, but the data eventually arrives intact. You might not notice 1–2% loss at all.
- Gaming, VoIP, video calls — These use UDP, which does not retransmit. Lost packets are simply gone. The application must either interpolate (guess what the missing data should have been) or play silence/freeze the frame. Even 0.5% loss is perceptible.
In a VoIP call, packets arrive every 20ms. At 1% packet loss, you're dropping roughly one packet every 2 seconds. Each dropped packet causes a 20ms audio gap. That sounds fine on paper — but in practice, the pattern of gaps is irregular and unpredictable, which is what makes it sound so disruptive. The human ear is far more tolerant of consistent latency than intermittent silence.
How Bad Is Your Packet Loss?
| Packet Loss | Rating | Gaming | VoIP / Video Calls | Streaming |
|---|---|---|---|---|
| 0% | Perfect | No impact | Crystal clear | No impact |
| 0.1–0.5% | Excellent | Imperceptible for most | Rare brief glitches | No impact |
| 0.5–1% | Acceptable | Occasional missed inputs | Noticeable audio dropouts | No impact |
| 1–2.5% | Problematic | Frequent missed shots, rubber-banding | Regular choppy audio, freezes | Rare rebuffering |
| 2.5–5% | Severe | Effectively unplayable competitively | Calls frequently unintelligible | Occasional rebuffering |
| > 5% | Critical | Unplayable | Connection unusable | Constant buffering |
What Causes Packet Loss
Packet loss can happen at any point along the network path between your device and the destination server — in your home, at your router, in your ISP's infrastructure, or at a transit network somewhere on the internet. Identifying where the loss is occurring is the key to fixing it. Here are every common cause, grouped by location.
Wi-Fi Interference and Congestion
The most common cause of packet loss for home users. When Wi-Fi collisions occur — two devices transmitting simultaneously — packets are corrupted and dropped. The 802.11 protocol handles some of this with CSMA/CA and ACK retransmissions, but at high congestion levels or with poor signal quality, packets get dropped at the radio layer before TCP even sees them.
Faulty or Substandard Cables
A damaged Ethernet cable, corroded RJ45 connector, or Cat5 cable running at Gigabit speeds causes intermittent transmission errors. The NIC and switch try to correct these errors, but errors that can't be corrected result in dropped frames. This type of packet loss is particularly insidious because it's sporadic — everything looks fine most of the time, then you get a burst of drops.
Overloaded or Failing Router / Modem
When a router's CPU is saturated, its packet buffers fill faster than it can process them. Once the buffer is full, incoming packets have nowhere to go and are dropped — this is the definition of bufferbloat-induced packet loss. It's distinct from hardware failure in that it only occurs under load. A failing modem or router (one with degrading hardware) can also cause random packet drops at any load level.
Faulty Network Interface Card (NIC)
A degrading NIC in your computer can corrupt packets at the hardware level before they even leave your machine, or drop incoming packets before the OS can process them. This is relatively rare but worth ruling out if all other causes have been eliminated — especially on older hardware or PCs that have been moved or dropped.
Last-Mile Connection Problems
The physical connection between your home and your ISP's equipment — the coaxial cable, DSL line, or fiber run — is a common source of packet loss. Degraded cable shielding, corroded splitters, water ingress into outdoor enclosures, and signal noise on copper lines all cause physical-layer errors that manifest as packet loss. Your ISP can measure signal quality remotely and in many cases can identify a problem without a home visit.
ISP Network Congestion
During peak hours, ISP network nodes — particularly the CMTS (cable) or DSLAM (DSL) aggregation equipment that handles hundreds of customers — can become overloaded. When a node's capacity is exceeded, it drops packets. This type of loss is time-dependent: it appears in the evenings and on weekends, and disappears during off-peak hours. If your packet loss tests show this pattern, the problem is in your ISP's infrastructure, not your home.
Routing and Peering Issues
Data between your home and a distant server travels through multiple autonomous networks (AS hops), each with its own equipment and peering agreements. Packet loss at a transit or peering point — where two networks exchange traffic — is common and often temporary. This type of loss usually affects only specific destinations (e.g., a particular game server or CDN) rather than all traffic uniformly.
Firewall Rules and Traffic Shaping
Some ISPs actively throttle or drop packets from specific applications — gaming, VoIP, or streaming — as part of traffic management policies or network neutrality violations. This type of loss is application-specific: you'll see loss on game traffic but not on a web browser test. A VPN will often route around this, which is a useful diagnostic tool as well as a potential fix.
How to Diagnose Packet Loss Step by Step
The diagnostic process is about systematically narrowing down where the loss is occurring. Work through these steps in order.
Measure your baseline
Run a 60-second test on jitter.is against Cloudflare. Note the packet loss percentage. Run it again at different times of day — morning, afternoon, and evening — to see if it's time-dependent. Time-dependent loss points to ISP congestion; constant loss points to hardware.
Isolate Wi-Fi vs wired
If you're on Wi-Fi, plug in an Ethernet cable and retest immediately. If packet loss drops to zero or near-zero on Ethernet, the problem is your wireless connection. If loss persists on Ethernet, the problem is in your home network or upstream.
Test at the router (bypass your home network)
Connect a device directly to your modem (bypassing your router entirely) and run the test. If packet loss disappears, the problem is your router. If loss persists, the problem is your modem or the ISP connection.
Run a traceroute to identify the losing hop
On Windows: tracert 1.1.1.1 — On macOS/Linux: traceroute 1.1.1.1. Look for hops where the reported latency jumps significantly or where you see * * * (timeouts) followed by a hop that responds normally. A hop that shows loss but all subsequent hops are fine is usually an ICMP rate-limit — not real packet loss. Loss that persists from a hop onward indicates the real problem location.
Test against multiple targets
Run tests against several different targets: Cloudflare (1.1.1.1), Google, your ISP's own servers, and a game server if applicable. If loss only appears on specific destinations, it's a routing or peering issue. If loss appears on all targets, it's in your home or last-mile connection.
Test over VPN
Enable a VPN and retest the same targets. If packet loss disappears over VPN, your ISP is actively filtering or throttling the traffic. If loss persists over VPN, the problem is in your local hardware or ISP's physical infrastructure.
Request an ISP line test
If loss persists on a wired connection directly to the modem, contact your ISP. Ask them to run a remote line quality test and report your uncorrectable error count, signal-to-noise ratio, and downstream/upstream power levels. Out-of-spec values indicate a physical plant problem that only the ISP can repair.
Fixing Packet Loss: By Cause
If the loss is on Wi-Fi
- Switch to Ethernet — eliminates the problem entirely in most cases
- Move to 5GHz or 6GHz band to reduce congestion and interference
- Change Wi-Fi channel to one that's less occupied in your area
- Move closer to the router to improve signal quality and reduce retransmissions
- Reduce the number of devices competing for airtime
If the loss is on a wired connection at home
- Replace all Ethernet cables — use Cat6 or better, check for physical damage
- Restart your router and modem — clear buffer and routing state
- Enable QoS to prevent buffer overflow under load
- Test with a different router to rule out hardware failure
- Test with a different NIC or USB-to-Ethernet adapter
If the loss is in the ISP's network
- Contact your ISP with timestamped test results from jitter.is
- Request a line quality test — ask about signal levels and error counts
- Escalate to a network engineer if first-line support is unhelpful
- If the loss is time-dependent (evenings only), specifically report "node congestion during peak hours"
- If the issue persists without resolution, file a formal service complaint or consider changing ISPs
When contacting your ISP about packet loss, bring data: the percentage of loss, which targets it affects, what times of day it occurs, and whether it appears on all devices or just one. Screenshots from jitter.is showing packet loss percentage over time are useful evidence. ISPs respond much faster to specific, documented technical complaints than to vague "my internet is bad" reports.
Measure your packet loss right now — the test takes 30 seconds and shows the exact percentage.
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Packet loss is one of the most damaging network problems for real-time applications, and even small percentages cause perceptible issues. Unlike high ping — which just means things are slow — packet loss means data disappears entirely, forcing applications to either guess or simply skip the missing content.
The diagnostic process is straightforward: test your baseline, isolate whether the loss is on Wi-Fi or wired, bypass your router to test the modem directly, run a traceroute to find which hop is dropping packets, and test against multiple targets to determine whether it's local or upstream. Each step narrows the problem to a specific layer that can be addressed with a specific fix.
In the majority of home setups, packet loss is caused by one of three things: Wi-Fi interference (fixed by Ethernet), a congested or aging router (fixed by restart, QoS, or upgrade), or a physical line issue (fixed by the ISP). Work through them in that order and you'll find the source.