H1B leftover period.

Hi Team,

I have a query regarding H1 left over period, my total H1 will end by 2019 August and i am planning to travel to India for one year starting next two months and had to work from India to my employer, want to know how my H1 left over period will be calcuated as my I797 is ending on 2019 August.

As per H1 policy will i be having 20months left over if i travel in next two months and return back on 2019 Jan.Please let me know.