Wifi is incredibly slow on OS X El Capitan

As per this article : How to troubleshoot Wi-Fi connectivity - Apple Support

Symptom: The Wi-Fi network seems slow

• Streaming movies may skip or pause.
• iTunes or other downloads may take an unusually long time to complete.
• Webpages may not load quickly.

Solution

If Internet access is slow on your computer, confirm your network supports the correct Wi-Fi standards. 802.11n provides the fastest Wi-Fi speeds. Other standards are fast, but you should confirm that your computer is using the fastest protocol available.

1. Hold the Option key while clicking the Wi-Fi menu.The PHY Mode line shows the protocol your computer is using to join the Wi-Fi network. If this does show the expected 802.11 protocol, you should check the settings of your Wi-Fi router. Consult the manufacturer of your router for information about configuring it.
2. Disable other active network services. Active network services consume a portion of the available bandwidth. Examples of these include file servers, video streaming, online games, and so forth. When these are in use, they may cause other services to slow down. Try turning off unused network applications to increase the speed of other applications. Be aware that other computers or devices connected to your network may also contribute to poor performance. If you are not sure if a computer associated with your Wi-Fi network is causing poor performance, try turning it off or disconnecting it from the network.
3. Use WPA2 Authentication, if available. The WPA2 authentication mode meets the highest standards for Wi-Fi compliance and should be used to provide the greatest speeds for modern Wi-Fi networks. Other authentication methods may reduce performance of your Wi-Fi network. In order to change the authentication method offered by your Wi-Fi router, you will need to contact the manufacturer.
4. Check your range to the Wi-Fi router and reduce the effect of interference. If your computer is too far from your Wi-Fi router or your environment has too much Wi-Fi interference, then your computer may not detect the Wi-Fi network properly. The easiest way to check for range limits with your Wi-Fi network is to move your computer or your Wi-Fi router closer together and make sure that there are no obstructions (such as walls, cabinets, and so forth) between the router and your computer.See Potential sources of wireless interference for more information about interference and solutions.
5. Try connecting to a different Wi-Fi network. If your computer works fine when connected to a different Wi-Fi network, then the issue may be related to your network router or ISP. In that case, contact the manufacturer of your router or your ISP.

Symptom: The network connection drops unexpectedly

• Your Mac may not not stay connected to your Wi-Fi network reliably.
• Your Mac may stop accessing the Internet during use.

Solution

Use these steps if your computer disconnects from its Wi-Fi network unexpectedly.

1. Check your range to the Wi-Fi router and reduce the effect of interference.If your computer is too far from your Wi-Fi router or your environment has too much Wi-Fi interference, then your computer may not detect the Wi-Fi network properly. The easiest way to check for range limits with your Wi-Fi network is to move your computer or your Wi-Fi router closer together and make sure that there are no obstructions (such as walls, cabinets, and so forth) between the router and your computer.See Potential sources of wireless interference for more information about interference and solutions.
2. Try connecting to a different Wi-Fi network. If your computer works fine when connected to a different Wi-Fi network, then the issue may be related to your network router or ISP. In that case, contact the manufacturer of your router or your ISP.

Symptom: After restarting or waking from sleep, my computer might not connect to the Internet

• After waking from sleep or starting up, your computer may not show that it is connected to a Wi-Fi network.
• After start or wake, your computer may indicate that it is connected to a network, but does not connect to the Internet.

Make sure you are not running Anti - virus , cleaners and other third party unidentified apps that could create more issues in the computer .

Oh man, PRAM flash to save the day. Couldn't be more grateful. I've wasted a couple days, bricked a new router while upgrading its firmware, only to realize it was my mutha flippin MBP. Come on, Apple!!

This is on Mid-2015 Retina MBP, so still very valid solution.

Gracias, Amigo!!

I recently came across this exact issue on my 2014 Mac Mini running 10.12.4.

I tried a number of the trouble shooting tips in here (reset PRAM, renew DHCP, forget the network etc), but they didn't solve the issue.

However, I was able to resolve the issue by unplugging all of my USB devices and found the culprit to be an external hard drive. I have no idea why this resolved it, but hopefully this can be added to the list of things people try!

Thank you thank you! I thought that this suggestion was a long shot, but BAM! It worked!

So far, my new wifi is fast again.

Hopefully, it will also help with the drag my MacBook was putting on the whole wifi system.

Go step by step by step and test.

1. Power off the router. Unplug it from the wall. Wait a while.

Plug it back to the wall. Power the router on. Wait until all the lights are lit properly. It will take a while.

Restart the computer.

Start up in Safe Mode.

https://support.apple.com/kb/PH18760?locale=en_US

2. Empty Cache.

Safari > Preference > Advanced

Checkmark the box for "Show Develop menu in menu bar".

Develop menu will appear in the Safari menu bar.

Click Develop and select "Empty Caches" from the dropdown.

3. Deselect Proxies if selected.

System Preference > Network > Advanced > Proxies Tab

Unlock the lock if you have to.

Under "Select Protocol", uncheck any box if checkmarked.

Click "OK" then "Apply”.

I'm also experiencing a significant drop in internet speed since upgrading to El Capitan. A second macbook (that's still on Yosemite) connected to the same router runs at normal speed.

I'm afraid I don't have a solution for you, but maybe some information that might be helpful in tracking one down...

I had awful wifi throughout most of Yosemite. Even after the fix that was supposed to be 10.10.4. Dropping signal. Ridiculously slow speeds after a few minutes. The need to turn wifi off and then on again, many times during the day. And it seemed to slow other machines on the network too.

But El Capitan -- for me -- has been a radical improvement. Our top speed where we are is 10.4 mbs and I consistently get above 9 mbs. This situation is only a few days old, of course, after a long miserable spring and summer.

But maybe it suggests that the problem for you might not be the new operating system, at least not exclusively.

Wish you the best of luck!

I am experiencing exactly the same problem. It is not limited to just one Wifi network. It happens both on my home and work network. Re-starting the router and/or my laptop (latest macbook pro) makes no difference!

What a complete load of rubbish. Come on Apple why do you keep making major releases with more holes than a swish cheese?

It smacks of incompetence or maybe you don't think you have to try that hard anymore?

I'm also having the same problem. Wi-Fi was working perfectly on Yosemite and Mavericks. I noticed that when I disable bluetooth, Wi-Fi speeds instantly increases, but I need bluetooth always on for instant hotspot and some accessories. So, I came back to Yosemite to wait for a fix. It's a shame for +1200$ (twice more on my country) machines having basic problems like that

We need to report this issue to Apple using Feedback Assistant located in /System/Library/CoreServices/Applications/Feedback Assistant.app

Same problems. Devices in the same area have downstream speeds of 18Mbps. Since updating to 10.11, the MacBook Pro (Retina, Mid 2012) has .7 to 2Mbps downstream.

Same problem here with MacBook Pro Late 2013 and Mac Mini 2012...

😕

I have similar problem after upgrading to El Capitan: Wifi speed decreased twice in LAN after upgrading to El Capitan