Owner Financing: Actual (realized) rate of return??

[Matt Holmer]

Good Morning-

There are a few duplexes in my local area that look great, but due to lack of funds for a down payment, seller financing might be an option.  The properties are owned free and clear.  Before I try to make a pitch, I want to make sure my thought process is correct.  I may be making this too complicated, but math has never been my strong suit.

Assumptions for this exercise:

$145,000 purchase price

$5000 down payment

$140,000 @ 5% interest, 30 year amortization

10 year balloon

Based on those numbers, the monthly PI would be $752.  After 120 months, the total in payments made would have been $90,240.00

Based on a 30 year amortization, the balloon payment would be $111,879.00

The total payments after 10 years is now: $207,119.00 (down payment + PI + Balloon)

So in 10 years there is a $62,119.00 increase in value of the seller's 145k.

Based on these numbers, what is the actual rate of return over the 10 year period?

Thank you for the assistance.