While the marginal tax on your wage earnings (assume for purposes of an example a rate of 24%) disappears with the deductibility of the interest expense of your home loan.
What does not disappear is the FICA levy on your wage which is split between wage earners and employer. Each paying 7.65% -when the Medicare levy of 1.45%, is added to the Social Security tax rate of 6.2%. The combined impost for a worker and your employer is thus 15.3% .
In respect of a home loan payment of $30,000 the amount lost to FICA in dollars is $4,590. The cost of your mortgage is therefore $34,590 – 15.3% higher than you were told by your Bank, Accountant and Financial Adviser.