Tax on Rental Income

Hi, Let out property  was vacant for 6 months of FY 2010-11. Monthly rent is Rs. 9000/-. So shall I consider my rental income as Rs. 54000/- for computation of ‘income from property’?  property tax would be Rs. 4000/- per year. So Net Annual Value would be Rs. 50000/- (ie., 54000-4000). Standard deduction @ 30% of Rs. 50000/- would be Rs. 15000/-. Housing loan interest is Rs. 115000/-. Hence loss of income from property is Rs. 80000/- (Rs 50000-15000-115000). Is this calculation correct? kindly help

regards

Kumar