How much can I borrow with a HELOC?

The formula is the one in the CFPB's HELOC booklet: take a percentage of the home's appraised value, then subtract the balance owed on the existing mortgage. The percentage is the lender's combined loan-to-value cap, and the booklet illustrates it at 75%. On a $500,000 home with $300,000 owed, that allows $375,000 of total borrowing against the house, and subtracting the mortgage leaves a $75,000 credit line.

The cap, not your equity, is the binding number. The same homeowner has $200,000 of equity, but the cap holds $125,000 of it in the house as the lender's cushion. Raise the cap and the line grows fast: at 80% of value the line is $100,000, and at 90%, $150,000. The cap control under the result shows the line at each level for your inputs; some lenders allow more than the booklet's illustration, and a few less.

Already owing more than the cap allows leaves no line at all, and owing more than the home is worth leaves no equity to borrow against. The calculator says which of those is true, with your numbers, rather than showing a zero without a reason.

A HELOC is two loans wearing one contract. During the draw period, typically about 10 years, you can borrow and repay freely and most lenders require interest only. On the default line of $75,000, fully drawn at 6.75%, that is $422 a month. The payment feels small because it is: the balance never falls.

When the draw period ends, the account converts to repayment and the balance must amortize to zero. Over the default 20-year repayment period the payment becomes $570 a month, a jump of $148. This is the section of the disclosure people skip and the number that surprises them a decade later. A shorter repayment period sharpens it: over 10 years the payment is $861.

The jump is the figure to budget against before opening the line, because it arrives exactly when the balance is at its largest and the interest-only habit is at its oldest. The calculator flags the jump whenever the repayment payment runs well past the interest-only one for your inputs.

HELOC rates float. Nearly all price at the prime rate plus a margin: prime is 6.75% on the Federal Reserve's H.15 release as of 2026-08-21, and the margin depends on your credit, the CLTV, and the lender. The default rate here is prime alone, so treat it as the floor of a real quote and add your margin on top.

Held at that rate with the line fully drawn from day one, the default line costs $50,625 of interest across the 10-year draw period, because interest-only payments retire nothing, and $61,866 more across the 20-year repayment period, $112,491 in all on $75,000 borrowed. That is the worst-case shape of the assumption, not a forecast: draw less, or later, and the interest falls with the balance.

The current combined loan-to-value at the defaults is 60.0%; fully drawn it rises to 75.0%, the cap itself. That ratio is why the line is secured debt at a rate far below a credit card: the house is the collateral, which is also the reason to price the repayment phase before borrowing against it.

Your actual rate path. HELOC rates are variable: they reprice when prime moves, and every payment on this page assumes the rate holds. A two-point rise in prime moves the interest-only payment proportionally, and the sensitivity table in the JSON twin prices that directly. The margin over prime is also yours, not the page's: it varies by credit score and lender and can be negotiated.

The fees. Many HELOCs carry an annual fee, some charge origination or appraisal costs, and some claw back closing costs if you close the line early. None of those are modeled. Nor is the lender's underwriting: a cap on paper does not guarantee approval, because the lender also qualifies your income and debt-to-income ratio against the payment.

This page models a line of credit, not a fixed home-equity loan; a home-equity loan disburses once at a fixed rate and amortizes from the first payment, so its arithmetic is the loan payment calculator's. The lender's disclosure is the binding figure; this page is for understanding it.

This calculator is built to be used without a browser. Every input is a query parameter on this page, and the same parameters on the JSON twin return the complete answer as a document.

GET /tools/heloc.json?value=650000&owed=280000

The response carries inputs after parsing and clamping, result with the credit line, the current and fully drawn CLTV ratios, the interest-only and repayment-phase payments with the jump between them, interest totals for both phases, plus sensitivity tables by CLTV cap and by rate, drivers ranked by effect with a plain sentence each, assumptions that say for every field whether you supplied it and which source the default came from, sources with URLs and as-of dates, warnings, a disclaimer, and in tool the canonicalUrl and jsonUrl that carry only your non-default parameters. The canonical URL is the answer's permanent address; use it when you cite the number.

Parameters, all optional, in any order:

• value ($), default $500,000.
• owed ($), default $300,000.
• maxCltv (%), default 75%, from CFPB, What you should know about home equity lines of credit.
• rate (%), default 6.75%, from Federal Reserve, H.15 Selected Interest Rates.
• drawYears (years), default 10 years.
• repayYears (years), default 20 years.

Values accept plain numbers and loose human formats such as 100k, $100,000, or 6.5%. Unknown parameters are ignored, values outside a field's range are clamped and reported in warnings, and the endpoint never fails on bad input. Responses are cacheable for a day; the defaults change when their sources publish, and tool.version changes when the method does.

• CFPB, What you should know about home equity lines of credit, as of 2014-01-01. Lenders commonly cap the credit line at a percentage, say 75 percent, of the home's appraised value, minus the balance owed on the existing mortgage.
• Federal Reserve, H.15 Selected Interest Rates, as of 2026-08-21. Bank prime loan rate 6.75 percent, week ending 2026-08-20.

Default values on this page: CLTV cap 75% (CFPB, What you should know about home equity lines of credit) and rate 6.75% (Federal Reserve, H.15 Selected Interest Rates, the bank prime loan rate). The home value, balance owed, draw period, and repayment period defaults are examples to be replaced.

Carlo is a personal finance agent. It knows your accounts, debts, and goals, so instead of a line on an example house it can tell you what drawing on your equity does to your payment load, your payoff order, and the other things you are working toward. Text it the question.

ask carlo anything(415) 376-5678