H1b transfer after approved I-140

Hi,

I have approved I-140 and got H1b extension for 2 years (till Oct 2016).

My question is, if I transfer my H1b to another employer how much extension period I would get with transfer. Is it same i.e. till Oct 2016 or I would get extension for next 3 years.

(I understand that new employer needs to apply for PERM and I-140 with same PD).

Thanks.