In my post ‘Kirk Wants a Free Down Payment Mortgage’ I re-ran the numbers from your original post. I have quoted from this post.

FT calculated the interest paid over 5 years correctly on the cash back mortgage at $67,595.35, however when he calculated the interest on the discounted mortgage he miscalculated and came to $49,499.01. The number he should have come up with was $52,104.19. This would have made the difference in interest paid over the 5 years $15,491.16, not the $18,096.34 that he calculated. Furthermore, when he went to calculate the annual return needed to grow the $10,000 enough to make up for the cost of borrowing it, he calculated the return needed to make $28,000, instead of $8,096.34 (the difference between the additional interest cost and the $10,000 cash received up front), which lead to a calculation of 23%. The actual rate of return required to recoup the additional interest cost had the $10,000 been invested would have been closer to 10.98%.

I checked, double checked, and triple checked these numbers, but if you have different calculations please let me know.

Kind regards,

Nolan