Second Mortgage Calculator

Calculate your combined first and second mortgage payments. See your combined LTV, total interest on both loans, and how much equity you can tap.

$
$
%
yrs
$
%
Combined Monthly Payment
$2,624
$1,880 first · $744 second
First Mortgage P&I: $1,880
Second Mortgage P&I: $744
First Mortgage (LTV)
62.2%
Combined LTV (CLTV)
75.6%
Available Equity
$170,000
Total Debt
$340,000
First Mortgage Interest
$329,276
Second Mortgage Interest
$29,270
Total Interest (Both Loans)
$358,546
Total Debt Cost
$698,546

How to Use This Second Mortgage Calculator

Enter your home value, first mortgage details, and the second mortgage you're considering to see your combined payment, combined LTV, and total interest costs.

Combined LTV (CLTV)

The key metric lenders use is Combined Loan-to-Value (CLTV): total debt divided by home value. Most lenders cap this at 80–85%. The calculator warns if your proposed second mortgage would exceed this limit.

Second Mortgage Rate

Second mortgages carry higher rates because they're in "second lien position" — if you default, the first lender gets paid first, making second mortgages riskier. Expect rates 1–2% above current first mortgage rates.

When to Choose a Second Mortgage vs. Cash-Out Refinance

A second mortgage preserves your existing first mortgage rate — critical if you locked in a rate below current market rates. If current rates are higher than your first mortgage rate, a second mortgage is almost always more cost-effective than a cash-out refinance.

Second Mortgage Payment Formula

First Monthly Payment = P1 × [r1(1+r1)^n1] / [(1+r1)^n1 - 1]

Second Monthly Payment = P2 × [r2(1+r2)^n2] / [(1+r2)^n2 - 1]

Combined Monthly = First Payment + Second Payment

CLTV = (First Balance + Second Amount) ÷ Home Value × 100

Max Second Mortgage = (Home Value × 0.85) − First Balance

Example: $450,000 home, $280,000 first mortgage (6.75%, 27 yrs remaining) = $1,853/mo. Add $60,000 second at 8.5% for 10 years = $744/mo. Combined = $2,597/mo. CLTV = 75.6%.

Example: Home Equity Loan for Renovation

The Nguyens Add a Primary Suite Addition

Their home has appreciated to $450,000, with $280,000 remaining on a 6.75% mortgage. They want $60,000 for a primary suite addition — but don't want to touch their 6.75% rate.

Home Value$450,000
First Mortgage Balance$280,000 at 6.75%
First Monthly Payment$1,853
Second Mortgage Amount$60,000 at 8.5%
Second Term10 years
Second Monthly Payment$744
Combined Monthly$2,597
CLTV75.6% (well under 85% limit)
Total Second Mortgage Interest$29,280

If they had done a cash-out refinance of $340,000 at current 7.25% rates, their monthly payment would be $2,320 — apparently less, but they'd lose their favorable 6.75% rate on the entire $280,000 balance and pay far more interest over the remaining loan life.

Frequently Asked Questions

A second mortgage is an additional loan taken against your home while your original first mortgage is still active. It's secured by the same property but in a subordinate (second) position. If you default and the home is foreclosed, the first mortgage lender gets paid in full before the second mortgage lender receives anything — hence the higher rate to compensate for that risk.
Most lenders limit your combined LTV to 80–85%. The formula: (Home Value × 0.85) − First Mortgage Balance = Maximum Second Mortgage. Example: $450,000 home × 0.85 = $382,500 − $280,000 first mortgage = $102,500 maximum second mortgage. Your credit score, debt-to-income ratio, and lender policies further affect the actual maximum.
Both are second mortgages, but structured differently. A home equity loan gives you a lump sum at a fixed interest rate with equal monthly payments — predictable and stable, great for a specific project. A HELOC (Home Equity Line of Credit) is a revolving credit line at a variable rate — you draw what you need when you need it. HELOCs have a draw period (usually 10 years) then a repayment period. Use home equity loans when you know the exact amount needed; HELOC for flexible, ongoing needs.
Second mortgage interest may be tax-deductible if the proceeds are used to buy, build, or substantially improve your home. If used for other purposes (paying off credit cards, vacations, car purchases), the interest is generally not deductible. The total mortgage debt eligible for deduction is limited to $750,000 for loans taken after December 15, 2017. Consult a tax professional for your specific situation.
The key question is: Is your current first mortgage rate lower than today's rates? If yes, keep your first mortgage and add a second — you preserve the lower rate on the larger balance. If your current rate is similar to or higher than today's rates, a cash-out refinance might be simpler. A rough break-even: if your current rate is more than 0.5% below current rates, a second mortgage is likely better. Our Refinance Calculator can help with the comparison.

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