The part of a house rent allowance that is not taxed, for someone paying rent, under the old regime.
The exempt amount is the least of three: the HRA actually received; rent paid minus 10% of salary; and 50% of salary if you live in Delhi, Mumbai, Kolkata, Chennai, Bengaluru, Hyderabad, Pune or Ahmedabad, or 40% elsewhere. "Salary" here means basic pay plus dearness allowance, not the whole CTC.
The rest of the HRA is taxable. The new regime gives no HRA exemption at all.
Figures on this page are filled from the same tax and scheme tables the calculators use, for the current financial year. Every term in the glossary.