H1B stay in US

Hi ,

I came to US on L1B in July 2010 and returned back to India in Nov 2010.

Then i entered US again in July 2011 and worked in US on L1B until Jan 2013.

I applied Change of status from L1B to H4 on 31st Jan 2013 .

I applied H1B in April 2013 while staying in US in H4 and got petition approved in Nov 2013 ( from Feb 2013 to Oct 2013 i was on H4 in US while waiting for H1B approval)

Currently My H1B visa is valid until Aug 2015.

I want to know if I can apply extention in Aug 2015 ? If yes what is the timeline my H1B can be extened for.

Thanks & Regards