The gross rental value of a property  in any income year shall be calculated as per the following formula,  namely:-  

a = (b+c+d)-e-f, where—

a = Total rental value,

b = the amount of rent received from the said property, or the annual value of the property, whichever is higher,

c = the amount in the nature of advance rent received from the said property in the said income year, by whatever name it may be called,

d = any other sum or any benefit received from the said property in the said income year, which is additional to the sum mentioned in “b” or “c”,

e =  any such advance, which was included in the total rental value on account of receipt in any previous income year, but such advance has been adjusted by the lessee against the rent of the relevant income year, 

f = vacancy allowance:

Provided that the non-availability of rental income shall be intimated to the Deputy Commissioner of Taxes by the 30th of every month.