This is not exactly correct. You can immediately go to your payroll department and change your W-4 withholdings and receive changes to your current payroll withholdings. Depending upon your company, this would become effective within a couple of payroll cycles. You would have less taxes taken out & thus be able put that towards your mortgage. With the deductions, you would owe less taxes next filing date. I assume your tax advisor would have calculated out the $800 amount you are quoting based on last year's income & this years projected earnings, as well as the deductions you will receive for the home ownership.