How long will El Capitan be supported with security updates?

[Luba]

How long will El Capitan be supported with security updates? I read on another thread 3 years and since El Capitan came out in 2015, Apple will stop with security updates in 2018?

I ask because my 2009 Mac Pro can't update to Sierra.

 

[redheeler]

Yes, each OS gets three years from launch with Apple supporting two prior versions in addition to the current. Based on Apple's current update schedule, support will drop in:
10.9 Mavericks - fall 2016
10.10 Yosemite - fall 2017
10.11 El Capitan - fall 2018
10.12 Sierra - fall 2019

But, from what I understand you can flash your 2009 Mac Pro 4,1 to a 5,1 and regain support for MacOS Sierra.

 

[dhstarr]

Yes, each OS gets three years from launch with Apple supporting two prior versions in addition to the current. Based on Apple's current update schedule, support will drop in:
10.9 Mavericks - fall 2016
10.10 Yosemite - fall 2017
10.11 El Capitan - fall 2018
10.12 Sierra - fall 2019

But, from what I understand you can flash your 2009 Mac Pro 4,1 to a 5,1 and regain support for MacOS Sierra.

I have a MACBook Pro Mid 2009, so I have the same problem. What does it mean to "flash" a MACBook?

 

[elf69]

I have a macbook pro 2009 on route to me.

There are guides here on flashing to get sierra to work.
Also guides on web.

see osxhackers.net for example

 

[redheeler]

I have a MACBook Pro Mid 2009, so I have the same problem. What does it mean to "flash" a MACBook?

I was referring to the desktop Mac Pro in response to the OP, not laptop MacBook Pro. For the MacBook Pro, you need to see this thread: macOS 10.12 Sierra Unsupported Macs Thread.