Best 2nd Mortgage Calculator
A second mortgage borrows against the equity in your home while your first mortgage stays in place. The honest question is not which lender is “best”; no calculator can know that without live quotes, and this page makes no lender claims. The computable question comes first: which loan structure fits your numbers? The same $50,000 costs strikingly different amounts as a fixed home equity loan, a HELOC, or a balloon loan, and this calculator runs all three from one set of inputs, alongside your available equity, your combined loan-to-value (CLTV), and the most you could borrow at the 85 percent CLTV cap most lenders work to.
It is pre-filled with a mid-market case: a $400,000 home, $250,000 still owed on the first mortgage, and a $50,000 second mortgage at 7.5 percent over 30 years. Press Calculate and the fixed loan prices at $349.61 a month with $75,859 of total interest, while the comparison table prices the other two structures from the same numbers. Replace them with your own and the whole picture, equity, cap, verdict, and comparison, moves together.
Estimates only. The HELOC figure is a model, not a quote: real HELOC rates vary, and payments depend on what you draw and when. The article below explains exactly how each structure is modelled.
Quick Answer
Key takeaways
- The 85% CLTV cap, not your raw equity, is usually the binding limit. The example home has $150,000 of equity but only $90,000 of borrowing room at the cap.
- Structure changes cost more than small rate differences do. On identical inputs, total interest runs from about $31,406 (HELOC model) to $112,500 (balloon, before its principal lands).
- A balloon loan’s low payment is borrowed time: $312.50 a month, then the full $50,000 is due at once.
- Every product here is secured by your home. The rate is lower than unsecured credit because the house is the collateral.
- Quick Answer
- What a second mortgage is, and where it stands in line
- The three numbers that decide everything
- Worked example: $50,000 three ways
- Reading the HELOC estimate honestly
- Which structure fits which job
- Closing costs, and the tax rule that changed
- What competing calculators miss
- Frequently asked questions
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What a second mortgage is, and where it stands in line
A second mortgage is a loan secured by your home taken while another mortgage is already secured by it. The Consumer Financial Protection Bureau calls these junior liens, and the word “second” is literal: if the home is sold to pay the debts, the first mortgage is paid first, and the second lender gets what is left. The CFPB’s explainer on what a second mortgage loan or junior lien is makes the consequence plain: second lenders carry more risk, so second mortgages price higher than first mortgages, and failing to repay can still cost you the home.
The two mainstream forms are the home equity loan (a lump sum at a fixed rate, repaid on a fixed schedule) and the HELOC (a revolving line at a usually variable rate, drawn as needed). The CFPB’s companion explainer on what a home equity loan is notes the fixed-rate lump sum is the predictable end of the market. The third structure in this calculator, the balloon loan, is the older and riskier pattern: small payments now, the whole principal at the end.
The three numbers that decide everything
Every result in the calculator is built from three calculations, in this order.
Combined loan-to-value (CLTV) = (first mortgage balance + second mortgage amount) / home value x 100.
Maximum at the 85% cap = (home value x 0.85) – first mortgage balance.
Fixed-loan payment = P x r x (1 + r)^n / ((1 + r)^n – 1), where r is the monthly rate and n the number of payments.
Watch which number binds. Borrowers usually anchor on equity (“I have $150,000 of equity, so I can borrow $150,000”), but the lender anchors on CLTV, because the cap protects them if prices fall. On the example home the cap allows $90,000, a full $60,000 less than the equity figure. Ask for more than the cap and most mainstream lenders decline or reprice, whatever your equity says. If the max-at-cap figure comes out negative, your first mortgage alone already exceeds 85 percent of the value, and a second mortgage is unlikely until the balance falls or the value rises.
Worked example: $50,000 three ways
All figures below are the calculator’s own outputs for the pre-filled inputs: $400,000 value, $250,000 first balance, $50,000 second loan, 7.5 percent, 30-year term.
| Figure | Value |
|---|---|
| Available equity ($400,000 – $250,000) | $150,000 |
| CLTV (($250,000 + $50,000) / $400,000) | 75.0% |
| Max at 85% CLTV cap ($340,000 – $250,000) | $90,000 |
| Fixed loan payment | $349.61 / month |
| Fixed loan total interest / total paid | $75,859 / $125,859 |
| Verdict | GOOD POTENTIAL |
| Structure (same inputs) | Monthly payment | Total interest | What else is due |
|---|---|---|---|
| Home equity loan (fixed) | $349.61 | $75,859 | Nothing: fully amortized |
| HELOC (variable, est.) | $562.50 (first month) | $31,406 | Nothing, if the modelled paydown runs |
| Balloon loan | $312.50 | $112,500 | $50,000 principal at the end |
The comparison teaches the real lesson of this page. The balloon looks cheapest monthly and is by far the most expensive overall, and it still owes you a $50,000 problem at the end. The HELOC model shows the least interest because its built-in principal paydown retires the balance in about 200 months rather than 360, so it front-loads principal into a higher first payment. The fixed loan is the middle path on every row: not the lowest payment, not the lowest interest, and the only one whose payment and end date are contractually certain.
Reading the HELOC estimate honestly
HELOCs are the hardest of the three to model, and this calculator’s approach is a deliberate simplification that you should understand before trusting its row. Real HELOCs have a draw period (commonly ten years) during which many lenders require only interest payments, followed by a repayment period. Rates are variable, tied to an index plus a margin, so the payment moves with the market.
The model here instead assumes you pay interest on the shrinking balance plus a principal allowance of 0.5 percent of the original amount every month. Two consequences follow. First, the term you enter does not change the HELOC totals: the balance retires in about 200 months (roughly 16.7 years) at that paydown rate, whatever term is selected. Second, the “monthly payment” shown is the first month’s; it declines as the balance falls. Treat the HELOC row as a disciplined-paydown scenario: what the line costs if you repay it like a loan instead of riding the draw period. If you plan to pay interest-only for ten years, your real interest total will be higher, and the jump when repayment starts is exactly the shock the CFPB’s Consumer Handbook on Adjustable Rate Mortgages teaches borrowers to stress-test. Borrowers who prefer a fixed payment on a variable-rate product can also weigh a 10-year adjustable-rate mortgage structure, where the rate is fixed for a decade before it can move.
Which structure fits which job
There is no best structure in the abstract; there is a best match between a structure and the shape of the expense.
Home equity loan (fixed)
- Fits: one expense with a firm price, like a roof or a renovation contract.
- Strength: payment and payoff date never move; budgeting is trivial.
- Cost: interest runs on the full amount from day one, even if you spend it slowly.
HELOC (variable)
- Fits: staged or uncertain expenses, like a phased remodel or tuition across years.
- Strength: you draw and pay interest only on what you use.
- Cost: variable rate means a payment you cannot fully predict; draw periods can end in a payment jump.
Balloon loan
- Fits: very little, for most homeowners. Sometimes short holds with a certain sale or refinance ahead.
- Strength: the lowest monthly outlay of the three.
- Cost: the highest total interest here, plus the full principal due at once, with refinancing risk if markets or credit move against you.
Beyond the structure, lenders underwrite the borrower. Expect a credit check (most want 620 or better, with the best pricing at 700 and above), income verification, and a debt-to-income test across all your payments, the same ratio a 45 debt-to-income ratio calculator measures against common lending thresholds. Approval for the structure you want also runs through an appraisal and the closing cost percentage on the loan, typically 2 to 5 percent of the amount, which this calculator leaves out of its totals so you can add your actual quote.
Closing costs, and the tax rule that changed
Two money details sit outside the calculator and change real-world comparisons. Closing costs on second mortgages typically run 2 to 5 percent of the loan amount for appraisal, origination, title, and recording. A “no-closing-cost” offer is not free money; the cost is usually recovered in the rate, which is why the CFPB advises comparing Loan Estimates on APR and total cost rather than headline fees, a process its loan estimate review guidance walks through line by line.
Taxes changed in 2018 and many borrowers still have the old rule in their heads. Under IRS Publication 936, interest on home equity debt is deductible only if the money is used to buy, build, or substantially improve the home securing the loan, and only within the overall mortgage debt limits ($750,000 for most filers on post-2017 debt). The IRS states the same condition in its Topic No. 505 on interest expense and in Publication 936 itself: equity borrowed for debt consolidation or spending does not qualify, whatever the loan is called. Whether you clear the bar for approval at all also depends on the lender’s ability-to-repay assessment, the standard behind the CFPB’s qualified mortgage rules, which is also why balloon features are barred from most qualified mortgages.
What competing calculators miss
Complete.tools’ second mortgage calculator prices only the fixed home equity loan and says so; there is no HELOC or balloon row to compare against. TrueValueCalc’s home equity loan page explains CLTV well but again computes a single structure. ToolHub’s home equity calculator answers “how much could I borrow” thoroughly, with a sensible limit table, then stops before pricing any structure. Lender tools like Achieve’s HELOC calculator price one product, the one that lender sells, and are built to start an application rather than a comparison.
This page computes the borrowing room and all three structures from one input set, prints the verdict logic it applies (insufficient equity, CLTV over 85 percent, or within typical requirements), and then does something the others do not: it tells you exactly where its HELOC model simplifies reality, and it refuses to rank lenders. Its limits are stated rather than hidden. No closing costs in the totals, no credit-score pricing tiers, and a HELOC estimate that assumes disciplined paydown. For a borrow decision, run your real numbers here to choose the structure, then take that structure to several lenders and compare their Loan Estimates on APR.
If the numbers come back tight, run the approval side too: an approved mortgage calculator frames how lenders weigh income and debts before they ever look at which structure you picked.
Frequently asked questions
A home equity loan is a lump sum with a fixed rate and a fixed payment that amortizes from day one. A HELOC is a revolving credit line, usually at a variable rate, that you draw on as needed; many are interest-only during a draw period of around ten years, then convert to repayment. Choose the loan for a known one-time expense with a firm price, and the line for expenses that arrive in stages or are hard to size in advance.
Most lenders cap your combined loan-to-value at 80 to 85 percent of the home's value. The borrowing room at an 85 percent cap is (home value x 0.85) minus your first mortgage balance. On a $400,000 home with $250,000 still owed, that is $90,000. Your raw equity on the same home is $150,000, which is why the cap, not the equity, is usually the binding constraint. Credit score, income, and debts can lower the approved figure further.
Typically 2 to 5 percent of the loan amount, covering appraisal, origination, title, and recording. Some lenders advertise no-closing-cost offers and recover the money through a higher rate instead, so compare offers on APR and total interest, not on the fee headline. This calculator does not add closing costs to its totals; add them yourself when you compare a real quote against its output.
Most lenders look for at least 620 for a home equity loan or HELOC, and the better rates cluster at 700 and above. A lower score does not always mean a refusal, but it usually means a lower CLTV cap and a higher rate. Because the loan is secured by your home, lenders weigh the equity cushion and your debt-to-income ratio alongside the score.
It can be, under narrow conditions. IRS Publication 936 says interest on home equity debt is deductible only when the proceeds are used to buy, build, or substantially improve the home that secures the loan, and the deduction is subject to the overall mortgage debt limits ($750,000 for most filers on newer debt). Borrowing to repay credit cards or take a trip does not qualify. Confirm your own situation with a tax professional before counting on the deduction.
Combined loan-to-value adds every loan secured by the home, including the new second mortgage, and divides by the home's value. Lenders underwrite the combined figure because it measures their total exposure if the home is sold. A first mortgage at a comfortable 62.5 percent LTV becomes a 75 percent CLTV after a $50,000 second loan on a $400,000 home, and it is the 75 percent that the second lender prices.
A balloon structure keeps payments low (interest-only in this calculator's model) and leaves the entire principal due as one large payment at the end of the term. On the worked example that means $312.50 a month and then $50,000 due at the end. The catch is refinancing risk: if rates are higher, your credit is worse, or the home is worth less when the balloon lands, you may have to sell to pay it. Federal rules also bar balloon payments from most qualified mortgages.
Yes. A second mortgage is secured by the home, and the Consumer Financial Protection Bureau warns plainly that failing to repay a home equity loan or line of credit can lead to foreclosure, even though the second lender is paid after the first in a sale. That is the core trade of every product covered here: lower rates than unsecured credit, in exchange for putting the house behind the debt.
No, and be wary of any page that claims to. This calculator compares loan structures, not lenders: it runs one set of your numbers through a home equity loan, a HELOC estimate, and a balloon loan, and shows the payment, total interest, and borrowing room for each. Which structure fits your situation is a real question with a computable answer. Which lender offers you the best rate is a shopping question that only live quotes can answer.
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References
- Consumer Financial Protection Bureau, “What is a home equity loan?” – defines the lump-sum fixed-rate structure and warns that upfront fees mean the monthly payment is not the whole cost. CFPB: What Is a Home Equity Loan?. Accessed October 2026.
- Consumer Financial Protection Bureau, “What is a second mortgage loan or junior-lien?” – explains second-lien position, why rates are higher, open-end versus closed-end structures, and the foreclosure risk. CFPB: What Is a Second Mortgage or Junior Lien?. Accessed October 2026.
- Consumer Financial Protection Bureau, “Consumer Handbook on Adjustable Rate Mortgages (CHARM booklet)” – the official guide lenders must give ARM applicants, covering index plus margin, rate adjustments, and payment shock. CFPB: Consumer Handbook on Adjustable Rate Mortgages. Accessed October 2026.
- Consumer Financial Protection Bureau, “What is a Qualified Mortgage?” – the ability-to-repay standard, including why balloon payments and interest-only features are excluded from most qualified mortgages. CFPB: What Is a Qualified Mortgage?. Accessed October 2026.
- Consumer Financial Protection Bureau, “Review loan estimates” – how to compare Loan Estimates across lenders, including the risky-feature disclosures for balloon payments and rate increases. CFPB: Review Loan Estimates. Accessed October 2026.
- Internal Revenue Service, “Topic No. 505, Interest Expense” – the rules for deductible mortgage interest, including the $750,000 debt limit on newer mortgages. IRS: Topic No. 505, Interest Expense. Accessed October 2026.
- Internal Revenue Service, “Publication 936, Home Mortgage Interest Deduction” – states that home equity interest is deductible only when proceeds buy, build, or substantially improve the securing home. IRS: Publication 936. Accessed October 2026.
- Federal Reserve Board, “What You Should Know about Home Equity Lines of Credit” (consumer guide, archived copy) – the classic Fed booklet comparing lines of credit with traditional second mortgage loans and listing plan costs and repayment options. Federal Reserve: Home Equity Lines of Credit Guide (archived). Accessed October 2026.
- Federal Reserve Board, “When Your Home Is on the Line: What You Should Know About Home Equity Loans” (consumer guide, hosted copy) – weighs home equity borrowing costs and risks, including the loss of the home on default. Federal Reserve: When Your Home Is on the Line. Accessed October 2026.
- LegalClarity, “What Are Balloon Loans? Definition, Risks, and Rules” – the statutory definition of a balloon payment and the qualified-mortgage restrictions that pushed balloon structures out of the mainstream market. LegalClarity: Balloon Loans, Definition, Risks, and Rules. Accessed October 2026.