Second Mortgage Calculator
Add a second mortgage to your existing loan and see the second-loan payment, your combined loan-to-value, and the total blended payment across both liens. Built for piggyback structures like 80-10-10 and 80-15-5 that keep the first mortgage at 80% to skip PMI.
First Mortgage
80% of the home's value.
Second Mortgage
Second liens price 1–3%+ above a first mortgage — the lender is paid after the first in a foreclosure.
Second Mortgage Monthly Payment
$492
$50,000 at 8.5% over 15 years.
Combined LTV (CLTV)
90.0%
$450,000 of $500,000
Total Blended Payment
$3,021
Both loans, principal & interest
Blended Rate
6.72%
Weighted across both liens
First Mortgage Payment (P&I)
$2,528
Second Mortgage Payment (P&I)
$492
80-10-10 structure — first mortgage stays at 80% LTV, no PMI.
Keeping the first lien at or below 80% of value is the whole point of a piggyback: the second mortgage covers the gap so you skip private mortgage insurance. Check what PMI would have cost with the PMI calculator.
Total interest on the second mortgage
Over the full 15-year term, before any extra payments.
$38,627
See exactly how the balance falls month by month with the amortization schedule.
Second Mortgage vs. HELOC
“Second mortgage” is an umbrella term for any loan that sits behind your first mortgage. It usually refers to a home equity loan: you borrow a fixed lump sum at a fixed rate and repay it on a set schedule, just like the calculator above models. A HELOC (home equity line of credit) is also a second mortgage, but it works like a credit card secured by your house — a revolving line you draw from as needed, usually at a variable rate, during a set draw period.
- Fixed vs. variable: a home equity loan locks the rate and payment; a HELOC rate typically floats with the prime rate, so the payment can rise.
- Lump sum vs. line: take a home equity loan when you know the exact amount you need (a piggyback down payment, a one-time renovation). A HELOC fits open-ended or phased spending where you draw over time.
- Piggyback fit: the second loan in an 80-10-10 is usually a fixed home equity loan, because the amount is known at closing and a fixed payment is easier to qualify around.
If you're weighing a line of credit against pulling cash out of a refinance, the HELOC vs. cash-out refinance comparison breaks down which is cheaper for your situation.
When Does a Piggyback Loan Make Sense?
A piggyback (80-10-10 or 80-15-5) trades one cost for another: you take a higher-rate second mortgage instead of paying private mortgage insurance. It wins when the second mortgage's cost is lower than PMI would be over the years you'll carry it — and there are a few situations where it clearly pays off:
- You're just short of 20% down. A 10% second mortgage bridges the gap so the first lien lands at exactly 80% LTV and PMI never attaches.
- You want to avoid a jumbo loan. Splitting the balance can keep the first mortgage under the conforming loan limit, qualifying it for lower conforming rates instead of jumbo pricing.
- PMI would be expensive or slow to cancel.Unlike PMI, a second mortgage's interest may be tax-deductible if used to buy the home, and the loan disappears when you pay it off rather than lingering until you hit an equity threshold.
The math flips against a piggyback when the second-mortgage rate is very high, when you'll reach 20% equity quickly (PMI cancels and the comparison shortens), or when you'd rather keep a single, simpler payment. Compare the piggyback's blended payment above against the PMI route with the PMI calculator before you commit.
How a Second Mortgage Affects Your Rate
A second mortgage doesn't change the rate on your first loan — that note is already locked. What it changes is the rate on the new money and your overall cost of borrowing. Because the second lien is repaid only after the first in a foreclosure, lenders price it higher, and two factors drive how much higher:
- Combined LTV. The higher your CLTV, the thinner the equity cushion behind the second lien and the higher its rate. Crossing 85% or 90% CLTV tiers typically bumps the rate up a notch.
- Credit score. Second-mortgage pricing is more credit-sensitive than first-mortgage pricing, so the same score gap costs you more on the second lien.
The calculator shows a blended rate— the weighted average across both loans — so you can see your true cost of borrowing rather than fixating on the second mortgage's headline number. A $50,000 second at 8.5% behind a $400,000 first at 6.5% only nudges the blended rate to roughly 6.7%, because the small, expensive loan carries little weight.
If your existing first-mortgage rate is high, that blended-rate view may reveal a cash-out refinance into a single loan is cheaper than layering on a second. If your first rate is low, leaving it alone and adding the second almost always wins.
Recommended reading
Books on home equity & refinancing
Borrowing against your home is one of the larger financial decisions you can make — these guides cover the mechanics, the tradeoffs, and the negotiating points so you walk into the conversation with the lender prepared.
The Home Equity Loan Handbook
Practical guides on tapping home equity
Plain-English explanations of how home equity loans, HELOCs, and cash-out refinances actually work — and how to compare offers without getting steered.
Mortgages For Dummies
Eric Tyson & Ray Brown
Covers refinancing, second mortgages, HELOCs, and the math behind each — useful background before you sign anything.
As an Amazon Associate this site earns from qualifying purchases. Links are sponsored.
Frequently Asked Questions
What is an 80-10-10 (piggyback) loan?
An 80-10-10 loan splits a home purchase into three pieces: a first mortgage for 80% of the price, a second mortgage for 10%, and a 10% cash down payment. The point is the 80% first lien — keeping it at or below 80% loan-to-value avoids private mortgage insurance, which conventional loans require whenever the first mortgage exceeds 80% LTV. An 80-15-5 works the same way with a larger second mortgage (15%) and a smaller 5% down payment, and an 80-5-15 flips those. The first number is almost always 80 because that's the PMI threshold.
Why is a second mortgage rate higher than my first mortgage?
A second mortgage sits behind the first in line. If the home is ever foreclosed and sold, the first-mortgage lender is paid in full before the second-mortgage lender sees a dollar — so the second lien carries more risk of loss and is priced accordingly. In practice, second-mortgage and home-equity rates typically run 1% to 3% or more above a comparable first mortgage, and the gap widens as your combined LTV climbs. Strong credit and a lower combined LTV are the two levers that bring the second-lien rate down.
What is combined loan-to-value (CLTV)?
Combined loan-to-value adds up every loan secured by the property and divides by the home's value. If you owe $400,000 on a first mortgage and take a $50,000 second mortgage on a $500,000 home, your CLTV is ($400,000 + $50,000) / $500,000 = 90%. Lenders cap CLTV on second mortgages — commonly 85% to 90%, sometimes up to 95% or 100% for well-qualified borrowers — because the higher the combined balance, the less equity cushion protects the second lien. CLTV, not the first mortgage's LTV alone, is the number a second-mortgage underwriter watches most closely.
Should I get a second mortgage or refinance my first?
It usually comes down to your existing first-mortgage rate. If you locked a low rate a few years ago, a cash-out refinance would replace that cheap loan with today's higher rate on the entire balance — often a bad trade. A second mortgage leaves the first loan untouched and adds a separate, smaller loan for just the money you need, so you keep the low rate on the bulk of your debt. If current rates are at or below your existing rate, a refinance that rolls everything into one loan can be simpler and cheaper. Run both with the refinance calculator before deciding.
Can I pay off a second mortgage early?
Almost always, yes. Most closed-end second mortgages (home equity loans) have no prepayment penalty, so extra principal payments shorten the term and cut total interest — check your specific note to be sure. Because second-mortgage balances are smaller and rates are higher, throwing extra money at the second lien first often saves more interest per dollar than prepaying the larger, cheaper first mortgage. Model the payoff with the amortization schedule to see how much interest early payments erase.