Assumable Mortgage
Compare a seller's low-rate FHA or VA loan against a new mortgage
Model the assumed first mortgage, the equity-gap financing, state-based tax and insurance defaults, and the new-loan alternative side by side. This is the cleanest way to see whether the low inherited rate still wins after the real-world friction is included.
Default scenario
$500,000 purchase, $320,000 assumed balance, 3.25% seller rate
Equity gap
$180,000
Sale price minus assumed balance.
Blended rate
5.14%
Weighted rate across first and gap financing.
Assumption fee
$1,600
VA default fee treatment.
Processing time
45-75 days typical
Allow slower contract timing than a standard purchase.
Verdict
The assumption route still wins, but the equity-gap structure matters a lot.
Compare the full carrying cost, not just the first-lien rate. The equity gap is what turns a headline story into a usable decision.
Monthly savings
$78/mo
Positive means the assumption wins.
Annual savings
$936
Monthly savings multiplied by 12.
Savings over remaining term
$25,285
Compared over 27 years.
Option A
Assume the seller's loan
$3,799/mo
Option B
Get a new mortgage
$3,877/mo
Rate and interest view
Blended assumption rate
5.14%
Weighted across the assumed first and the gap loan.
New-loan comparison rate
6.75%
Fresh 30-year market-rate scenario.
Interest on assumed first
$161,081
Across the remaining 27-year term.
Interest on new loan over same window
$590,533
Interest paid on the new mortgage during the same comparison period.
Methodology
How this assumable mortgage calculator works
The first comparison is mechanical. The calculator takes the seller's remaining balance, the inherited interest rate, and the remaining term to produce the assumed first-mortgage principal-and-interest payment. It then calculates the equity gap between the sale price and the remaining balance and prices that gap separately using your chosen rate and term. Those two pieces together show the financing burden of the assumption path before taxes and insurance are added back in.
The new-loan side uses the same sale price but applies your down payment percentage to create a new 30-year mortgage amount. The calculator then adds state-based property tax, homeowners insurance, and PMI when the down payment is below 20%. That makes the comparison closer to an actual housing-payment decision rather than a headline-rate comparison that hides the carrying costs buyers still have to qualify for.
The most important thing to remember is that the low assumed rate does not automatically win. A very attractive assumed first mortgage can still lose if the equity gap is so large that the second-lien payment becomes punitive. That is why the calculator highlights the blended rate and the full monthly payment instead of implying that the first-mortgage coupon alone answers the question.
Questions
Frequently asked questions
What is an assumable mortgage calculator?
It compares taking over a seller’s existing FHA or VA loan against getting a brand-new market-rate mortgage. The comparison includes the assumed first mortgage, any equity-gap financing, property tax, insurance, PMI on the new loan, and the one-time assumption fee.
Why does the equity gap matter so much?
The equity gap is the difference between the home’s sale price and the seller’s remaining loan balance. Buyers have to cover that gap with cash, a second mortgage, or seller financing, and the cost of that gap often determines whether the low assumed rate still wins.
Can a non-veteran assume a VA loan?
Yes. A civilian can assume a VA loan if the servicer approves the file, but the seller’s VA entitlement usually stays tied to the property until payoff unless a veteran buyer substitutes entitlement.
Does assuming a mortgage reset the term back to 30 years?
No. An assumption keeps the seller’s remaining balance, rate, and remaining term. If the seller has 27 years left, the buyer takes over a 27-year remaining schedule rather than starting a fresh 30-year amortization.
How long does a mortgage assumption usually take?
A well-documented assumption usually takes about 45 to 75 days, which is slower than a standard purchase loan and should be reflected in contract timelines.
Related guides
What to read after the calculator
Use these guides to pressure-test whether the low inherited rate is really better than the alternatives available to you.
Assumable mortgage guide
Learn the rules, timeline, and equity-gap tradeoffs before you shop for an assumption.
Mortgage points calculator
Compare assumption savings against the cost of buying down a new loan rate.
Refinance calculator
Useful if the seller’s low-rate loan is not assumable and the alternative is improving the financing later.
15-year vs 30-year guide
Pressure-test how the shorter remaining assumed term compares with a fresh 30-year loan.
Closing costs explained
Pair the assumption fee with the rest of the transaction-cost stack.
DTI guide
See how taxes, insurance, PMI, and the gap loan affect qualification.