Wrap-Around Mortgage Calculator

A wrap-around mortgage is one of the most misunderstood instruments in real estate, and one of the most powerful for a seller who knows what they are holding. The premise is simple enough to explain in a sentence: the seller keeps their old, cheap mortgage alive and sells the property on a new, larger note at a higher rate, pocketing the difference. The mechanics underneath that sentence are where the money is made, and where the risk lives.

Understanding Wrap-Around Mortgage Arbitrage

Picture a seller who owes $180,000 on a mortgage locked at 4% years ago. That loan is an asset now, not a liability, because nobody is writing 4% paper today. The seller could pay it off and walk away with their equity. Or they could leave it in place and sell the property for $300,000 to a buyer who cannot qualify at a bank, taking $30,000 down and carrying a $270,000 note at 7.5%.

Here is what just happened. The seller collects 7.5% on the full $270,000 the buyer owes, while continuing to pay only 4% on the $180,000 underlying loan. The 3.5-point spread on that $180,000 is pure arbitrage, money the seller earns on the bank's capital rather than their own. On top of that, the seller earns the full 7.5% on the $90,000 of their own equity still in the deal. Stack those two together and the return on the seller's actual invested capital climbs far above the 7.5% printed on the note. The buyer gets financing they could not otherwise obtain; the seller gets a yield no bank deposit or bond will touch. That is the engine, and it runs on the gap between an old rate and a current one.

How to Calculate Your Blended Return on Equity

The face rate of the new note tells you almost nothing about what the seller actually earns. The number that matters is the return on equity, and it is built from a spread, not a rate.

Start with the seller's trapped equity: the sale price minus the down payment minus the existing balance. In the example, $300,000 less $30,000 less $180,000 leaves $90,000. That $90,000 is the seller's real skin in the game, the capital that did not come back at closing and is now working inside the wrap.

Next, take the monthly payment the buyer makes on the new note and subtract the payment the seller still makes on the underlying loan. The difference is the monthly cash flow spread. Annualize it, divide by the trapped equity, and you have the blended return on equity.

The reason this figure routinely lands in the double digits, well north of the note rate, is leverage. The seller is earning a spread on the entire underlying balance using none of their own money for that portion, then earning the full note rate on the slice of equity they did leave in. Divide a payment spread that reflects interest on $270,000 by an equity base of only $90,000 and the percentage is naturally amplified. This is the same principle that makes any leveraged investment punch above its coupon, expressed here in the language of owner financing.

Risk Management Framework for Wrap Sellers

The arbitrage is real, but it is not free, and a seller who treats a wrap as easy money tends to learn the risks the expensive way. Three of them deserve sober attention before any note is signed.

The due-on-sale clause. Nearly every institutional mortgage written in the last forty years contains a due-on-sale clause, which gives the lender the contractual right to demand the entire balance the moment the property is transferred without their consent. A wrap transfers possession and equitable title to the buyer while leaving the underlying loan untouched and unpaid. If the lender discovers the transfer, it may call the loan due in full. Sellers and their counsel manage this risk in various ways, but none of them make it disappear. Pretending the clause does not exist, or assuming it will never be enforced because rates have risen and lenders are watching transfers more closely than they did in the soft-rate years, is how a profitable wrap becomes a forced refinance or a foreclosure. Go in with eyes open and structure the deal knowing the lender holds this card.

Servicing mechanics. The single most important operational safeguard on a wrap is that the underlying loan gets paid first, every month, without fail. The cleanest way to guarantee this is to never let the buyer's money pass through the seller's hands. A third-party loan servicing or escrow company collects the buyer's full payment, remits the payment on the underlying mortgage directly to the original lender, and forwards the remaining spread to the seller. This does three things at once: it documents the payment history for both parties, it ensures the senior debt is always current regardless of the seller's own discipline, and it gives the buyer confidence that their payments are actually protecting their position. Skipping the servicer to save a small monthly fee is a false economy. If the seller pockets the buyer's payment and falls behind on the underlying note, the buyer can be current and still lose the property to a foreclosure they did not cause.

Default protocols. Before the deal closes, the note and the wrap agreement must spell out exactly what happens when the buyer stops paying, because some buyers will. The instrument used matters: a wrap structured as an all-inclusive trust deed or contract for deed carries different remedies and timelines than a standard note and mortgage, and the right choice depends on the state. The agreement should define the cure period, the late-payment triggers, and the foreclosure or forfeiture path with precision, so the seller can act quickly to protect the underlying loan if payments stop. Speed matters here for a specific reason: the seller remains personally liable on the original mortgage no matter what the buyer does. Every month the buyer is in default is a month the seller may have to service the underlying debt out of pocket to keep it from going delinquent. A well-drafted default protocol is what lets the seller move before that bleeding starts.

A wrap-around mortgage rewards the seller who respects the structure and punishes the one who treats it casually. Run the numbers, retain counsel who has closed these in your state, use a licensed servicer, and never lose sight of the fact that the underlying lender can change the game at any time. Handled with that discipline, the wrap turns a dormant low-rate mortgage into one of the highest-yielding instruments a private seller can hold.