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Turning a cheap rate into a dollar figure
A below-market rate feels good. This lesson makes it a number — and names the point where the math stops mattering because an appraisal won't support the price.
Suppose the reference-deal buyer gets an 8% seller-financed rate on $295,000 (the $315,000 price less a $20,000 down payment) instead of the roughly 7% a conventional lender would charge that same buyer today. That one-point spread is worth something specific and calculable — not just 'a good deal.' The value of favorable terms is the present-value gap between the seller's actual note and a hypothetical market-rate loan on the same amount and term, discounted back to today.
Two things determine how large that gap is: how wide the rate spread is, and how long the buyer actually expects to hold the note before selling or refinancing. A one-point spread held for two years is worth far less than the same spread held for the full term, because the value only accrues for as long as the buyer is actually paying the below-market rate instead of a market one.
What 'overpay' means, and its limit
Once you know what the terms are worth in dollars, you can translate that into purchase-price headroom: the maximum amount a buyer could roll into a higher price and still come out even against a market-rate loan at the original price. This is the calculation a lot of creative-finance pitches gesture at without ever running — 'the terms justify a higher price' is a claim; the present-value gap is the number that either backs it up or doesn't.
Watch out — The wall this hits: the appraisal
Financed overpay only works up to what an appraisal will support if the buyer ever needs to refinance the note into conventional financing — and appraisals price the property, not the terms it was bought under. A buyer who rolls the full theoretical terms-value overpay into the contract price can end up unable to refinance at all, because the appraised value comes in below what they agreed to pay. Treat the overpay figure as an upper bound to negotiate under, not a target to hit exactly.
There's a second cost that's easy to forget when converting terms value into price headroom: a higher contract price usually means a higher transfer tax and, in states that reassess property tax at sale, a higher ongoing tax bill for as long as the buyer owns it. Net the terms-value gain against those before deciding how much of it is worth capturing in the price versus simply taking as a lower monthly payment instead.
What discount rate to use
The single biggest lever in this entire calculation is the discount rate you choose to price the note at, and there's no universally correct answer — it should reflect the actual risk of the payer and the property, not a round number picked out of habit. A rate near current mortgage rates assumes the buyer is nearly as reliable as a bank borrower; a rate closer to hard-money lending assumes real default risk. Running the same note at 6% and at 12% can produce present values that differ by tens of thousands of dollars on an otherwise identical deal — which is exactly why the tool below lets you try more than one rate rather than committing to a single answer.