Least/minimum of the following is exempt (Not taxable/deducted from total HRA received)
(a) Actual amount of HRA received
(b) Rent paid Less 10% of salary
(c) 50% of salary if house taken on rent is situated in Kolkata, Chennai, Mumbai and
40 % of salary if the house is taken on rent is NOT situated in Kolkata, Chennai, Mumbai and Delhi.
Click here to calculate taxability of House Rent Allowance.
For details:-House rent allowance calculator (incometaxindia.gov.in)
Source:- Income tax website.