How is the Zakat calculated on a property mortgaged to the bank?

Real estate designated for housing is not subject to zakat (definition). However, if it is designated for trade and profit, its value is assessed at the price on the day zakat is due, and 2.5% of this value is to be given, provided it reaches the nisab (definition) and a full year has passed over it. The fact that the property is mortgaged does not affect this. As for real estate designated for rent, zakat is not obligatory on its value; rather, it is obligatory on the saved rental income, provided it reaches the nisab and a full year has passed over it.