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Assumable Mortgage Calculator

With loan assumptions being a lot more common these days, I decided to build an assumable mortgage calculator.

It allows you to compare an assumable mortgage versus a home loan at today’s market rates, which are quite a bit higher.

For example, you might be able to assume someone’s existing 30-year fixed set at 2.75% instead of settling for a new loan today at 6.75%.

That results in real savings, though there is the assumption gap to consider, which is the difference between the outstanding loan balance and sales price.

Fortunately, my calculator figures this all out for you and provides a side-by-side analysis to help you determine if it’s worthwhile.

Assumable Mortgage Calculator

Compare taking over a seller’s existing VA, FHA, or USDA loan against getting a brand-new mortgage at today’s rate — including the assumption fee and the cash you’d need to cover the seller’s equity.

The Assumable Loan

Determines the estimated assumption fee
$
%
yrs
Years left on the seller’s amortization
$
Auto-estimated from loan type — editable
$

Covering the Equity Gap

The purchase price is usually higher than the loan balance you’re assuming — that difference is the seller’s equity, and you’ll need to cover it with a down payment, a second mortgage, or both. Enter the cash you’ll put down below, and we’ll calculate how much second mortgage (if any) covers the rest.

Equity Gap to Cover
—
$
The rest is financed with a second mortgage
%
To finance any remaining gap
yrs

New-Loan Alternative

$
%
%
Optional — used to date payoff

Full Comparison

Remaining Balance Over Time

Amortization Schedule

Disclaimer: This calculator is for informational and educational purposes only and does not constitute financial, legal, or tax advice. VA, FHA, and USDA loans are generally assumable with lender/servicer approval; most conventional loans are not, due to due-on-sale clauses. Assuming a VA loan does not require the buyer to be a Veteran, though the seller’s entitlement may remain tied to the property unless a VA-eligible buyer substitutes their own entitlement. Assumption fees are estimated only (a 0.5% VA funding fee on the remaining balance; HUD’s current $1,800 maximum FHA processing fee, which most servicers now charge since it was raised from $900 in 2024; a rough flat estimate for USDA) and vary by servicer; actual fees, credit/income qualification requirements, and processing timelines (commonly 45–120 days) should be confirmed with the loan servicer. The second mortgage used to help cover the seller’s equity is modeled as a simple fixed-rate, fully amortizing loan at the rate and term you enter; real second mortgages (home equity loans, HELOCs, or seller financing) may have different structures, such as interest-only periods or variable rates, that aren’t reflected here. FHA loans generally carry mortgage insurance premiums (MIP) for the life of the loan at the original rate, which is not included in this comparison. New-loan figures reflect principal and interest only and do not include typical closing costs. Consult your loan servicer and a licensed mortgage professional for your exact terms.

How to Use the Assumable Mortgage Calculator

First you enter in the loan type, whether it’s an FHA loan, VA loan, USDA loan, or another less common type of assumable mortgage.

This will auto-calculate the estimated assumption fee. Next enter the remaining loan balance, the home seller’s mortgage rate, and the remaining loan term.

Remember, even if it was a 30-year fixed, it might only have 24 years left on it.

Lastly, enter the home purchase price.

Once you’ve done that, the calculator auto-computes the equity gap, which is the difference between the purchase price and outstanding loan balance.

[Searching for a home loan? See your options with dozens of lenders fast.]

You’ll need to cover this shortfall, either with a cash down payment and/or a combination of cash and a second mortgage.

It’s pretty common to do either, though those with limited assets will need to take out a concurrent second mortgage, such as a home equity loan or home equity line of credit (HELOC).

Once you enter in your proposed down payment, it will calculate the second mortgage amount needed.

Enter an interest rate and loan term for the second mortgage to get an accurate monthly payment. They sometimes have terms less than 30 years, so be sure to estimate properly.

The final section is the new loan comparison if you don’t assume a mortgage. So you must enter a proposed down payment, mortgage rate, and loan term.

There’s an optional field to enter your purchase date to see the proposed loan payoff as well. Otherwise it defaults to the current date.

From there you’ll see the total monthly principal and interest payment of the assumed loan versus a regular loan.

You’ll see the monthly savings, the total interest and total cost of each loan, and the payoff dates of each loans.

In addition, you can see your remaining loan balance over time with each loan, along with an amortization schedule that compares both loans.

These visuals should make it easier to determine which path is right for you, and if assuming a loan instead of taking out a new one makes good financial sense.

One thing to consider is that a home might be priced higher if the seller has an assumable loan they think provides value. But even so it can be well worth assuming!

Just be patient as loan assumptions can take a while, sometimes over 90 days, while a regular mortgage generally takes 30 to 45 days.

Colin Robertson
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