Second Mortgage Calculator

Say your home is worth $450,000, you still owe $280,000 on your first mortgage, and your lender caps total borrowing at an 85% combined loan-to-value (CLTV). That means the lender will allow up to $382,500 of total debt against the home, so about $102,500 is available for a second mortgage. Borrow $50,000 of it on a 15-year fixed loan at 8.5%, and the payment is roughly $492 per month. This second mortgage calculator does both halves of that math: how much equity you can tap, and what the new payment costs.

How much you can borrow (the CLTV formula)

Lenders limit a second mortgage by your combined loan-to-value - the total of every loan secured by the home divided by the home's value. The amount available for a second mortgage is:

With a $450,000 home, an 85% cap gives $382,500 of allowable debt. Subtract the $280,000 first-mortgage balance and $102,500 remains for a second mortgage. Raise the cap to 90% and you unlock $125,000; drop it to 80% and only $80,000 is available. The CLTV limit is set by the lender and the loan program, not by you.

How the monthly payment is calculated

A fixed-rate second mortgage (home equity loan) amortizes just like a first mortgage, using the standard formula on the second loan amount:

where P is the second loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of payments (years × 12). The calculator then splits each payment into interest and principal so you can see the balance fall year by year.

How to use this calculator

You only need five numbers to get a realistic estimate. Work through the fields in order:

1. Current home value: use a recent appraisal or a conservative market estimate. Lenders rely on their own appraisal, so do not overstate it.
2. First mortgage balance: enter what you still owe on your primary loan today, not the original amount.
3. Max combined LTV: the lender's cap. The default is 85%; use the 80/85/90 buttons to test different programs.
4. Second loan amount: how much you want to borrow. Tap "Use max available" to fill in the most the CLTV cap allows.
5. Rate and term: enter the quoted rate and pick a term from 5 to 30 years.

Press Calculate to see the monthly payment, your available equity, total interest, your new combined LTV, and a year-by-year amortization schedule.

Who this calculator is for

• Homeowners with built-up equity who want a lump sum without refinancing their low-rate first mortgage.
• Renovators pricing out a major project funded by a home equity loan.
• Debt consolidators weighing a fixed second mortgage against higher-interest credit cards.
• Buyers using a piggyback loan who want to size an 80/10/10-style second loan to avoid PMI.
• Anyone comparing a fixed lump-sum second mortgage against a variable HELOC.

Why a second mortgage instead of a refinance?

If your first mortgage carries a low rate, a cash-out refinance would replace that whole balance at today's higher rates - an expensive trade. A second mortgage leaves the first loan untouched and adds a separate, smaller loan on top. You pay a higher rate on the second piece only, not on the entire balance, which is often cheaper overall when first-mortgage rates have risen since you bought.

Worked example: tapping equity for a renovation

You own a $500,000 home with a $300,000 first mortgage and want $60,000 for a kitchen and bath remodel. At an 85% CLTV cap the lender allows $425,000 of total debt, leaving $125,000 available - more than enough. Borrow the $60,000 on a 15-year fixed second mortgage at 8.5% and the payment is about $591 per month, with roughly $46,400 of interest over the full term. Your new combined LTV becomes ($300,000 + $60,000) / $500,000 = 72%, comfortably inside the cap.

Scenario comparison: same loan, different terms

Borrowing $50,000 at 8.5%, here is how the term changes the payment and lifetime interest:

• 10-year term: about $620/month, with roughly $24,400 in total interest - higher payment, far less interest.
• 15-year term: about $492/month, with roughly $38,600 in total interest - a middle ground.
• 20-year term: about $434/month, with roughly $54,200 in total interest - lowest payment, most interest paid.

A longer term lowers the monthly payment but you pay substantially more interest over the life of the loan. Choose the shortest term whose payment still fits your budget.

Key terms explained

• Second mortgage / home equity loan: a fixed lump-sum loan secured by your home, repaid in equal installments behind the first mortgage.
• CLTV (combined loan-to-value): all loans against the home divided by its value. The main limit on how much you can borrow.
• Lien position: the order lenders are repaid in a sale or foreclosure. The second mortgage is in second position, which is why it costs more.
• Available equity: the borrowing room left under the CLTV cap after subtracting your first-mortgage balance.
• Amortization: the schedule that splits each payment into interest and principal until the balance reaches zero.
• Piggyback loan: a second mortgage taken at purchase to reduce the first loan below 80% and avoid PMI.

What changes the result the most

• CLTV cap: the single biggest driver of how much you can borrow - 80% vs 90% can change availability by tens of thousands.
• Home value: a higher appraised value raises the allowable debt and your available equity.
• First mortgage balance: the more you still owe, the less room remains for a second loan.
• Interest rate: second mortgages price higher than firsts, so the rate has a strong effect on the payment.
• Term length: stretching the term lowers the payment but increases total interest.

Tips for a stronger second-mortgage application

• Borrow less than the maximum when you can - staying well under the CLTV cap often earns a better rate.
• Shop several lenders; CLTV limits, rates, and fees differ, and a higher cap may unlock the amount you need.
• Use a recent, realistic home value; the lender's appraisal, not your estimate, sets the final numbers.
• Match the term to the purpose; a short term for debt payoff, a longer one only if cash flow is tight.
• Budget the combined payment (first + second), not just the new loan, before you commit.

Limitations and assumptions

This calculator is a planning estimate, not a loan quote. Keep these assumptions in mind:

• It models a fixed-rate lump-sum second mortgage; it does not handle variable-rate HELOCs or interest-only draw periods.
• It calculates the second loan only and excludes your first-mortgage payment, property tax, insurance, and HOA.
• It does not include closing costs, lender fees, or points, which can add to the upfront cost.
• The CLTV cap is the value you enter; real limits depend on the lender, loan program, credit score, and occupancy.
• Your actual approval and rate depend on a current appraisal, credit, and debt-to-income ratio - shop several lenders to compare real offers.

How it compares to related calculators

This page answers "how much can I borrow as a second mortgage and what will it cost?" If you have a different question, a sister tool fits better:

• For a revolving, variable-rate line of credit instead of a lump sum, use the HELOC Calculator.
• To estimate the payment on a primary home loan, use the Mortgage Calculator.
• To compare replacing your current loan against keeping it, use the Refinance Calculator.
• For a full payment-by-payment breakdown of any loan, use the Amortization Calculator.
• To find your maximum purchase price, use the Home Affordability Calculator, and to plan a deposit, the Down Payment Calculator.

Sources

• Consumer Financial Protection Bureau (CFPB) - What is a second mortgage loan or "junior-lien"?
• Consumer Financial Protection Bureau (CFPB) - What is a home equity loan?
• Consumer Financial Protection Bureau (CFPB) - Owning a Home: mortgage basics.