HELOC Calculator
Available credit line from your equity, and the monthly cost interest-only versus repayment. 100% free, no signup. Everything runs in your browser.
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A HELOC is a credit line secured by your house, and the two questions that matter are how big a line you can get and what drawing on it costs each month. This calculator answers both. Enter your home value, your current mortgage balance, and the maximum combined loan-to-value your lender allows (I default to the common 80 to 85 percent range, editable like everything else), and it shows your estimated available credit. Then enter a draw amount and a rate, and it shows the monthly cost two ways: interest-only, which is how most HELOCs work during the draw period, and full repayment.
The math runs entirely in your browser, nothing is uploaded, and there is no signup. I added the two-payment view because interest-only numbers look deceptively gentle, and I have watched that gentleness surprise people ten years later when the repayment period starts.
How to use
- Enter your current home value. A recent appraisal, a comparable sale, or a realistic online estimate all work as a starting point.
- Enter your remaining mortgage balance from your latest statement.
- Set the maximum combined LTV your lender allows. If you have not applied yet, 80 or 85 percent are common ceilings.
- Read your estimated available credit line, which is the LTV cap times home value minus the mortgage balance.
- Enter how much you plan to draw and an interest rate to see the interest-only monthly cost.
- Compare that against the fully amortizing payment over a repayment term you choose, so you see both phases of the loan.
Why use our heloc calculator?
The credit line math is simple, but people constantly get it wrong by forgetting the existing mortgage. If your home is worth 500,000 dollars and the lender caps combined LTV at 85 percent, total debt against the house can be 425,000. Subtract a 300,000 mortgage and your maximum line is about 125,000. This calculator makes that chain visible instead of just printing an answer.
Interest-only payments are the sharp edge of HELOCs. During the draw period, often the first ten years, most lenders require only interest, which keeps payments low while the principal sits untouched. When repayment starts, the payment can jump substantially. I show both numbers side by side because choosing a HELOC while looking only at the interest-only figure is choosing blind.
Two more honest notes. Almost all HELOCs carry variable rates tied to the prime rate, so the payment you calculate today is a snapshot, not a promise, and the rate field is editable precisely so you can test higher scenarios. And the line is secured by your home, which means falling seriously behind can put the house itself at risk. The CFPB's HELOC explainer covers the mechanics and the protections in plain language.
All outputs here are estimates, not financial advice, and lender-specific rules like minimum draws, rate floors, and annual fees will move the real numbers. A HELOC is also not the only way to reach your equity. Compare it against a cash-out refinance, and use the loan comparison tool if you are weighing a fixed home equity loan against the line. Whichever way you lean, your home value and mortgage balance stay in this browser tab, unlogged and unshared.
Who is this tool for?
Budgeting a renovation. If the kitchen quote is 60,000 dollars, check whether your equity supports the line at your lender's LTV, then look at what carrying that balance costs monthly at today's rate and again a couple of points higher.
Setting up a standby credit line. Plenty of homeowners open a HELOC and draw nothing, treating it as cheap-to-hold emergency capacity. The calculator tells you how big that standby line could plausibly be before you apply.
Bridging between houses. Some buyers draw against the current home for the next home's down payment, then repay from sale proceeds. Model the monthly carrying cost here and cross-check the amount against my down payment calculator to size the draw.
Rate stress testing. Because the rate is just an editable number, you can answer the question a variable-rate product demands: what happens to my payment if prime rises two points while I am carrying this balance.
Frequently asked questions
As a rule of thumb, take your home value, multiply by the lender's maximum combined LTV (commonly 80 to 85 percent), and subtract your mortgage balance. Lenders then layer on credit score, income, and debt requirements, so treat the calculator's figure as a ceiling estimate rather than an approval.
The draw period, often ten years, is when you can borrow from the line and usually pay interest only. The repayment period, often twenty years after that, is when borrowing stops and payments include principal. The jump between the two is exactly why this calculator shows both payment styles.
Almost always variable, typically tied to the prime rate plus a margin, though some lenders offer fixed-rate locks on portions of the balance. Because the rate moves, run the payment math at today's rate and at a higher one before you commit.
It depends on your existing mortgage. If you are sitting on a low fixed rate, a HELOC leaves it untouched while a cash-out refinance replaces it entirely. If your current rate is high, refinancing might win. Run both scenarios, and remember that neither my math nor anyone's blog post is financial advice.
The line is secured by the house, which is exactly why the rate is far lower than a credit card. Serious default can lead to foreclosure, the same as a mortgage. Borrow accordingly, especially for spending that does not build any equity back.
No, only on what you actually draw. An open line with a zero balance usually costs nothing monthly, though some lenders charge annual or inactivity fees, which is worth checking before you open one as a standby.
No. The calculator is local JavaScript. Your home value and balances never leave your browser, no account is required, and the tool works offline once the page has loaded.