Should a mortgage be treated as loan and hence be deducted from net worth when calculating zakat?

> A mortgage loan, or simply mortgage, is used either by purchasers of real property to raise funds to buy real estate, or alternatively by existing property owners to raise funds for any purpose, while putting a lien on the property being mortgaged. > Mortgage Loan , Wikipedia I've read somewhere it is better to consider the amount for Zakah which is going to be paid immediately. Whereby the people I have talked to in general say that all Zakat is deferred until you are free of loans. **Question:** Should all of the amount be treated as loan and hence reduce from net worth, or only calculate zakat on what you need to pay in a year?