Assumable Mortgage Checker: Could You Take Over the Seller’s Low-Rate Mortgage?
About one in five outstanding US mortgages still carries a rate below 3% (Redfin analysis of the FHFA National Mortgage Database, Q3 2025). Some government-backed loans let a buyer assume the seller’s loan — keeping its rate — instead of getting a new one at today’s rates. This checker tells you whether the loan qualifies, what you’d save, and the catch nobody mentions.
Heads up: every input below describes the seller’s existing loan, not a loan you’d take out. Listing agents often advertise “assumable loan” in the listing description.
How to find these homes: Search listings for the word “assumable” (some sites have a filter), or ask the listing agent two questions: what type of loan does the seller have, and what’s the remaining balance? Agents on low-rate listings usually know — it’s a selling point.
What the process looks like: You apply to the seller’s loan servicer (not a new lender), qualify with normal credit/income/DTI checks, and wait — assumptions typically take 45–90 days, longer than a regular mortgage. Fees are low: usually $500–$1,500 (the math below uses the $1,000 midpoint, plus the 0.5% VA funding fee on VA loans).
What you’ll get below: Whether the loan can transfer at all, what you’d actually pay each month vs a new loan, and the equity-gap math that determines whether this is realistic for your cash.
✓ Likely assumable (FHA)
FHA loans are assumable with lender approval. You’ll need to qualify (credit, income, DTI) just like a normal mortgage, and pay an assumption fee (typically $500–$1,500).
Assume @ 3.10%
$1,448/mo
P&I on $310,000 · 26 yrs left
New loan @ 6.40%
$2,252/mo
P&I on $360,000 · 30 yrs, cash as down payment
Assuming saves $803/mo — $96,406 over 10 years
Simple sum of 120 monthly differences, before investing or discounting. Money saved in year 10 is worth less than money saved today, and if you invested each month’s difference the total would be higher.
These two loans don’t run the same length
The assumed loan has 26 years left; a new loan starts a fresh 30. You own the home free and clear 4 years sooner — and you’re paying down principal faster the whole time. The monthly figures above can’t show that, because a shorter term makes the payment higher, not lower. Total interest is where it shows up:
Interest to payoff — assume
$141,913
over 26 yrs on $310,000
Interest to payoff — new loan
$450,656
over 30 yrs on $360,000
Assuming costs $308,743 less in interest across the life of the loan — a much bigger number than the monthly gap suggests, because it captures both the lower rate and the shorter term.
Both figures assume you hold each loan to payoff and never refinance. They are nominal totals, not discounted. The loan balances differ ($310,000 vs $360,000), so this is not an apples-to-apples rate comparison either — it’s what each path actually costs you.
The catch: the equity gap
Assuming the loan only covers the seller’s balance. The difference between the $420,000 price and the $310,000 balance — $110,000 — is the seller’s equity, and you must cover it in cash or with expensive second-lien financing.
Seller’s equity$110,000
Assumption fee$1,000
Cash needed$111,000
Assumption fee uses the $1,000 midpoint of the typical $500–$1,500 servicer range. Not included: title, escrow, inspection, appraisal, or prepaid taxes and insurance — budget a few thousand more.
Your $60,000 covers 54% of the $111,000 needed — you’re $51,000 short. Options: negotiate the price down, a second mortgage (at market rates, eating into the savings), or seller financing for the gap.
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The bigger question
A 3.10% rate changes the entire rent-vs-buy equation. Run the full month-by-month analysis with the assumed rate and see what it does to your 10-year net worth.