Why Is My Internet So Slow? The 7-Step Diagnosis Ladder (Cheapest Test First)
A diagnosis ladder for slow internet: seven usual suspects ranked by probability, the two-minute DNS check, and the exact evidence pack that makes ISPs act.
Quick answer: Slow internet has exactly seven usual suspects: the plan itself, Wi-Fi, bufferbloat, congestion windows, background hogs, old hardware, or the ISP’s route. This ladder walks them in cheapest-test-first order — most people find their culprit by step four.
The diagnosis ladder (run top to bottom)
- Baseline the line. Ethernet (or sit next to the router) and run Toolfyra Internet Speed Test. Write down down/up/ping/jitter. This number divides the world in two: line problems start here; in-home problems appear later.
- Compare to your plan. Below ~60% of promised on ethernet, three runs at three hours = ISP-side evidence (skip to step 7). At or above plan? Your line is fine — the slowness is in-home (steps 2-6).
- Kill the hogs. Check every device for sync clients, updates, torrent boxes, streaming tablets. Router admin pages show per-device traffic on most modern firmware. Re-test.
- Test Wi-Fi properly. Run the same test in the slow room vs next to the router. Under 50% of baseline = coverage/interference — work the Wi-Fi guide.
- Test under load for bloat. Start a big download, re-test latency. 5x+ spike = bufferbloat — fix it here.
- Reboot with intent. Router off 30 seconds (not 5 — let lines reset), then modem, then device. If speed returns for a day and decays again, hardware or ISP provisioning is implicated.
- Escalate with evidence. Three timed screenshots (morning/evening/night), ethernet noted, plan number circled. Support teams respond to evidence, not adjectives.
The seven suspects, ranked by how often they are guilty
| # | Suspect | Signature | Fastest test |
|---|---|---|---|
| 1 | Wi-Fi, not the line | fast wired, slow wireless | room-by-room tests |
| 2 | Background hogs | slow only sometimes | router traffic page |
| 3 | Bufferbloat | fine idle, dies under load | test during a download |
| 4 | Evening congestion | slow 7-11 pm only | three timed runs |
| 5 | Old router/hardware | fine after reboot, decays | 48-hour pattern |
| 6 | VPN/proxy left on | slow everywhere, all day | toggle off, re-test |
| 7 | ISP line fault | below plan on ethernet always | evidence + ticket |
The two-minute DNS and browser sanity check
Sometimes "internet slow" is "this browser is slow": a 2013 laptop with 40 tabs, extension bloat, or a DNS resolver timing out and retrying. Swap DNS to 1.1.1.1 or 8.8.8.8 for a day, try a second browser or device on the same Wi-Fi. If the other device is fast, the network just got exonerated.
When the evidence says ISP: the escalation template
Support needs: plan number, three timed results (hours noted), method (ethernet, tool used, MB transferred), and the ask (line check / oversubscription review / modem replacement). One paragraph, screenshots attached. This template resolves more tickets than any amount of complaining — and if the ISP cannot fix it in 30 days, that same document justifies a provider switch or contract-exit request.
Prevention: the quarterly 10-minute routine
- Re-run the three-test series each quarter; trends beat snapshots.
- Firmware updates on router/modem twice a year.
- Re-audit sync/backup schedules after new devices join the home.
- Re-test after any plan change — "upgraded to 500" often silently changes nothing. See why results differ before celebrating.
FAQ
Why is my internet so slow all of a sudden? Newest suspect first: a device started a backup, an update window opened, or the ISP changed provisioning. The ladder finds it in minutes.
Why is Wi-Fi slow but ethernet fast? Congratulations — your line is fine. Radio diagnosis: the Wi-Fi guide.
Can a slow DNS make everything feel slow? Yes — page starts hang on lookups while downloads still fly. Swap resolver and compare page-start feel.