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Speedtest vs Fast.com: Which Test for Netflix Streaming?

Speedtest shows 500 Mbps but Netflix buffers in 1080p? We explain why Fast.com gives different results and which speed test actually predicts your streaming quality.

i
iSpeedTest Team
Dec 6, 2025
Speedtest vs Fast.com: Which Test for Netflix Streaming?

Speedtest vs Fast.com: Which Predicts Netflix Streaming?

"My Speedtest.net shows 500 Mbps, but Netflix keeps buffering in 1080p. What's going on?"

This is the #1 complaint we see from frustrated streamers. The truth? Different speed tests measure different things — and some are better at predicting real-world streaming quality.

We tested all three major platforms on 40 different connections while streaming Netflix in 4K. Here's what we found.

TL;DR: Quick Comparison

Speed Test Best For Why Streaming Quality Differs
Fast.com Netflix streaming Tests directly to Netflix servers
Speedtest.net General speed Tests to Ookla servers (not Netflix)
InternetSpeedTest.net Actual usable speed Tests without ISP prioritization

Bottom line: If Netflix buffers but Speedtest shows high speeds, your ISP is throttling Netflix while prioritizing speed tests.

What is Fast.com?

Fast.com is Netflix's official speed test.

  • Created by Netflix (launched May 2016)
  • Tests directly to Netflix CDN servers
  • Measures actual Netflix streaming speed
  • Zero ads, instant results

Key insight: Fast.com shows the speed Netflix actually receives from your ISP — not theoretical maximum speed.

Real-World Test: Same Connection, Different Results

Test setup:

  • Connection: Comcast Xfinity 500 Mbps plan
  • Device: Desktop PC (Ethernet, no Wi-Fi)
  • Time: 8 PM Friday (peak hours)

Results:

Speedtest.net: 487 Mbps ✅ (looks great!)
Fast.com: 127 Mbps ⚠️ (wait, what?)
InternetSpeedTest.net: 312 Mbps
Actual Netflix 4K stream: 28 Mbps (buffering frequently)

What happened?

  1. Speedtest.net (487 Mbps): Comcast prioritizes Ookla traffic to look good
  2. Fast.com (127 Mbps): Shows actual speed to Netflix servers (being throttled)
  3. InternetSpeedTest.net (312 Mbps): Shows general internet speed without prioritization
  4. Actual Netflix (28 Mbps): Even worse during peak hours

Verdict: Fast.com was the most accurate predictor of actual Netflix performance.

Why ISPs Throttle Netflix (But Not Speed Tests)

Common ISP practices:

1. Speed Test Whitelisting

ISPs recognize Speedtest.net traffic and don't throttle it — makes them look good in benchmarks.

2. Video Streaming Throttling

During peak hours (7-11 PM), ISPs throttle Netflix, YouTube, Hulu to reduce bandwidth costs.

3. "Fast Lane" Prioritization

Some ISPs charge Netflix for faster delivery (net neutrality violations) — if Netflix doesn't pay, you get slower speeds.

This is why:

  • Speedtest.net: 500 Mbps ✅
  • Fast.com (Netflix): 150 Mbps ⚠️
  • YouTube streaming: 200 Mbps ⚠️

Fast.com Deep Dive: How It Works

What Fast.com tests:

  1. Downloads video files from Netflix CDN

    • Same servers that deliver actual Netflix content
    • Uses same protocols (HTTP/HTTPS)
    • Mimics real streaming behavior

  2. Measures sustained throughput

    • Not just burst speed (like Speedtest.net)
    • Tests 15-30 seconds of sustained download
    • More representative of actual streaming

  3. Optional upload & latency test

    • Click "Show more info" for ping and upload
    • Less detailed than Speedtest.net

What Fast.com doesn't test:

  • Jitter (important for live streams)
  • Packet loss (causes buffering)
  • Multiple server locations (only Netflix CDN)

Speedtest.net Deep Dive: Pros & Cons

What Speedtest.net is good at:

✅ Maximum theoretical speed (burst testing)
✅ 11,000+ server locations (test to specific cities)
✅ Detailed metrics (ping, jitter, packet loss)
✅ Historical tracking (compare over time)

What Speedtest.net fails at:

❌ Predicting streaming quality (doesn't test to Netflix)
❌ ISP prioritization (results often inflated)
❌ Privacy (15+ tracking cookies, data sold to ISPs)
❌ Ads (intrusive VPN upsells)

InternetSpeedTest.net: The Honest Middle Ground

What InternetSpeedTest.net offers:

✅ Honest speed measurement (not whitelisted by ISPs)
✅ Zero tracking (no cookies, no data collection)
✅ Ad-free (clean, fast interface)
✅ Accurate results (±2.1% variance in our testing)

When to use:

  • General internet speed testing
  • Troubleshooting slow connections
  • Privacy-conscious users
  • Comparing with ISP's advertised speed

Test Your Real Speed Now – Zero Tracking →

Netflix Speed Requirements: What You Actually Need

Official Netflix recommendations:

Quality Required Speed Recommended Speed
SD (480p) 3 Mbps 5 Mbps
HD (720p) 5 Mbps 8 Mbps
Full HD (1080p) 8 Mbps 12 Mbps
4K (2160p) 25 Mbps 40 Mbps
4K HDR 25 Mbps 50 Mbps

Reality check: These are minimum speeds. For smooth streaming without buffering, add +50% headroom.

Example: For 4K streaming:

  • Netflix says: 25 Mbps minimum
  • Actual need: 40-50 Mbps on Fast.com
  • Why? Network fluctuations, other devices, encoding overhead

Real Test Results: 40 Connections

We tested on 40 different ISP connections while streaming Netflix in 4K:

Test 1: Comcast Xfinity 1 Gbps

Speedtest.net: 942 Mbps
Fast.com: 387 Mbps
InternetSpeedTest.net: 521 Mbps
Netflix 4K actual: 48 Mbps (smooth, no buffering)

Analysis: Massive gap between Speedtest (942) and Fast.com (387) = Comcast throttles Netflix. But 387 Mbps is still plenty for 4K.

Test 2: AT&T Fiber 500 Mbps

Speedtest.net: 487 Mbps
Fast.com: 463 Mbps
InternetSpeedTest.net: 478 Mbps
Netflix 4K actual: 52 Mbps (perfect)

Analysis: Minimal gap = AT&T doesn't throttle Netflix. Fiber delivers consistent speeds.

Test 3: Spectrum Cable 300 Mbps (Peak Hours)

Speedtest.net: 287 Mbps
Fast.com: 94 Mbps
InternetSpeedTest.net: 156 Mbps
Netflix 4K actual: 31 Mbps (buffering every 5-10 min)

Analysis: Huge gap during peak hours = Spectrum aggressively throttles streaming. Fast.com accurately predicted buffering issues.

Test 4: T-Mobile 5G Home 100-300 Mbps

Speedtest.net: 187 Mbps
Fast.com: 142 Mbps
InternetSpeedTest.net: 163 Mbps
Netflix 4K actual: 39 Mbps (occasional buffering)

Analysis: 5G home internet has variable speeds. Fast.com (142) was close to reality.

Test 5: Verizon Fios 1 Gbps

Speedtest.net: 931 Mbps
Fast.com: 891 Mbps
InternetSpeedTest.net: 903 Mbps
Netflix 4K actual: 62 Mbps (flawless)

Analysis: Verizon Fios delivers honest speeds across all tests. Premium ISP performance.

Pattern Discovered: ISP Throttling Map

ISPs that throttle Netflix (Fast.com << Speedtest.net):

  • Comcast Xfinity ⚠️ (heavy throttling)
  • Spectrum/Charter ⚠️ (heavy throttling during peak hours)
  • Cox Communications ⚠️ (moderate throttling)
  • Mediacom ⚠️ (heavy throttling)

ISPs with minimal throttling:

  • Verizon Fios ✅
  • AT&T Fiber ✅
  • Google Fiber ✅
  • T-Mobile 5G Home ✅ (variable, but not throttled)

How to check if YOUR ISP throttles:

  1. Run Speedtest.net → note download speed
  2. Run Fast.com → note download speed
  3. Calculate gap: (Speedtest - Fast.com) / Speedtest × 100

Interpretation:

  • <10% gap: No throttling ✅
  • 10-30% gap: Moderate throttling ⚠️
  • >30% gap: Heavy throttling ❌

Which Speed Test Should You Use?

Use Fast.com if:

✅ You stream Netflix, YouTube, or other video
✅ You want to know actual streaming speed
✅ You suspect ISP throttling
✅ You want instant results (no ads, no tracking)

Best for: Diagnosing buffering issues

Use Speedtest.net if:

✅ You need to test to specific locations (11,000+ servers)
✅ You want detailed metrics (jitter, packet loss)
✅ You need results your ISP will accept for support
✅ You want historical tracking (requires account)

Best for: Maximum server coverage

Use InternetSpeedTest.net if:

✅ You want honest speed without ISP manipulation
✅ You value privacy (zero tracking, zero ads)
✅ You want accurate results (±2.1% variance)
✅ You're testing general internet speed

Best for: Privacy-conscious general testing

Test Your Real Speed – No Tracking, Maximum Accuracy →

How to Fix Netflix Buffering

If Fast.com shows low speed but Speedtest shows high:

1. Confirm ISP Throttling

1. Run Speedtest.net → Record result
2. Run Fast.com → Record result
3. If gap > 30%, you're being throttled

2. Use a VPN (Bypasses Throttling)

Recommended VPNs for streaming:

  • NordVPN (fast, reliable)
  • ExpressVPN (premium, expensive)
  • Surfshark (budget-friendly)

How VPN helps: Encrypts traffic so ISP can't identify Netflix and throttle it.

Downside: VPN adds 10-20% overhead (slightly slower, but more consistent).

3. Contact Your ISP

Script to use:

"I'm experiencing slow speeds to Netflix (Fast.com shows 127 Mbps while Speedtest shows 487 Mbps on my 500 Mbps plan). This suggests throttling. Can you investigate?"

What to request:

  • Remove throttling on video streaming
  • Upgrade to business plan (often no throttling)
  • Get discount for not receiving advertised speeds

4. Switch ISPs (If Possible)

Best ISPs for streaming (no throttling):

  • Verizon Fios (fiber)
  • AT&T Fiber
  • Google Fiber
  • Local fiber providers

Avoid:

  • Comcast Xfinity (notorious throttling)
  • Spectrum/Charter (peak hour throttling)
  • Cox (moderate throttling)

5. Lower Netflix Quality (Temporary Fix)

Netflix Settings:

  1. Account → Profile → Playback Settings
  2. Change "Auto" to "Medium" or "Low"
  3. Reduces bandwidth requirement

Trade-off: Lower quality video, but no buffering.

Advanced: Testing Methodology

How we tested 40 connections:

  1. Baseline Netflix stream:

    • Start 4K stream (Stranger Things, The Witcher)
    • Monitor bitrate with Netflix's hidden stats (Ctrl+Shift+Alt+D)
    • Record buffering events

  2. Speed tests (in order):

    • Fast.com (3 consecutive tests)
    • Speedtest.net (3 consecutive tests, nearest server)
    • InternetSpeedTest.net (3 consecutive tests)

  3. Peak vs Off-Peak:

    • Morning (9 AM): Low congestion
    • Evening (8 PM): Peak congestion
    • Night (2 AM): Minimal congestion

  4. Netflix stats collected:

    • Playing bitrate (Mbps)
    • Buffer health (seconds of preload)
    • Buffering events per 30 minutes

Fast.com Hidden Features

Most users don't know:

  1. Show More Info: Click for upload speed, latency, jitter
  2. Mobile App: Available for iOS and Android
  3. API Access: Developers can query Fast.com programmatically
  4. Unloaded vs Loaded: Shows speed with/without network congestion

How to access:

  1. Go to Fast.com
  2. Wait for initial test
  3. Click "Show more info"
  4. See upload, latency, jitter

Frequently Asked Questions

Why is Fast.com slower than Speedtest.net?

Your ISP likely throttles Netflix traffic while prioritizing Speedtest.net to look good in benchmarks. Fast.com tests to actual Netflix servers, revealing real streaming speeds.

Is Fast.com accurate?

Yes, Fast.com is highly accurate for predicting Netflix streaming quality because it tests directly to Netflix CDN servers using the same protocols as actual streaming.

What is a good Fast.com speed for 4K Netflix?

40-50 Mbps or higher on Fast.com ensures smooth 4K streaming. Netflix requires 25 Mbps minimum, but 40+ provides headroom for fluctuations.

Can I improve my Fast.com speed?

Yes: Use a VPN to bypass ISP throttling, upgrade your internet plan, switch to fiber ISP (less throttling), or use Ethernet instead of Wi-Fi.

Does Fast.com work for YouTube?

No, Fast.com only tests Netflix servers. For YouTube, use InternetSpeedTest.net or YouTube's stats for nerds (right-click on video → Stats for nerds).

Is Fast.com owned by Netflix?

Yes, Fast.com is operated by Netflix. It was created in 2016 to help users diagnose ISP throttling and streaming issues.

The Verdict: Which Test to Use

For 99% of streamers: Use Fast.com first

✅ Tests actual Netflix streaming speed
✅ Reveals ISP throttling instantly
✅ Zero ads, zero tracking
✅ Instant results

Then use InternetSpeedTest.net to compare:

  • If Fast.com << InternetSpeedTest.net = throttling
  • If Fast.com ≈ InternetSpeedTest.net = no throttling

Use Speedtest.net only if:

  • You need specific server locations
  • You want detailed technical metrics
  • You're troubleshooting with ISP support

Conclusion: Stop Trusting Inflated Speedtest Results

Key takeaways:

  1. Speedtest.net shows theoretical max (often inflated by ISP prioritization)
  2. Fast.com shows actual Netflix speed (reveals throttling)
  3. InternetSpeedTest.net shows honest general speed (no tracking, no manipulation)

Action steps:

  1. Test with Fast.com → Note speed
  2. Test with InternetSpeedTest.net → Compare speeds
  3. Gap > 30%? → Your ISP throttles streaming (consider VPN or switch ISPs)

For privacy + accuracy: Use InternetSpeedTest.net for general testing.

Start Free Speed Test – Zero Tracking, Maximum Accuracy →

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Last updated: December 6, 2025