Common mortgage calculation mistakes

The most common errors are:

1. Calculating from the property price instead of price - down payment.
2. Forgetting that cash is also needed for appraisal, notary, taxes and fees.
3. Entering a 9% annual rate as 9 or 0.09 per month instead of 0.09/12.
4. Comparing only the payment while ignoring term and total interest.
5. Treating the calculator’s principal-and-interest result as the all-in housing cost.
6. Never inspecting the amortization schedule or final balance.

Use consistent principal, rate and term inputs; retain decimals; add external costs separately; and compare with the lender’s formal schedule. The last amortization row should reach zero, with a final-payment adjustment if necessary.

Validate the base scenario with the mortgage calculator.