HELOC Calculator

Say your home is worth $450,000 and you still owe $250,000 on the mortgage. If your lender allows a combined loan-to-value (CLTV) of 85%, you can borrow up to $382,500 against the home; subtract the $250,000 you already owe and your available credit is $132,500. If you draw $50,000 at an 8.5% rate, the interest-only payment during the draw period is about $354 per month, and once the line converts to a 20-year repayment, the amortized payment rises to about $434 per month. This HELOC calculator shows all three numbers so you can see both what you can borrow and what it will cost.

How available credit is calculated

A HELOC is limited by your combined loan-to-value ratio. The formula is:

where Max CLTV is the highest combined loan-to-value your lender permits (commonly 80%-90%). The more equity you hold and the higher the allowed CLTV, the larger your line. Drawing money raises your combined LTV, so the calculator also shows where you land after the draw.

Draw period vs. repayment period

A HELOC works in two phases. During the draw period - typically 5 to 10 years - you can borrow, repay and re-borrow up to your limit, and most lenders require only interest payments on the outstanding balance. The interest-only payment is simply the balance multiplied by the monthly rate (annual rate ÷ 12). When the draw period ends, the repayment period (often 10 to 20 years) begins: you can no longer draw, and the balance amortizes into fixed principal-and-interest payments. Because principal is now included, the payment jumps - this is the "payment shock" many borrowers overlook.

Variable rates and how they affect your payment

Most HELOCs carry a variable interest rate tied to an index, such as the prime rate, plus a fixed margin. When the index moves, your rate and payment move with it. A 1% rate increase on a $50,000 balance adds roughly $42 to a month of interest-only payments. Because the rate is not locked, it is wise to stress-test your budget against a higher rate, keep your CLTV well below the lender's cap, and avoid drawing the full line just because it is available.

HELOC vs. home equity loan

A HELOC is a revolving line you draw from as needed, usually at a variable rate - good for ongoing or uncertain costs like a multi-stage remodel. A home equity loan is a lump sum at a fixed rate with set payments from day one - better when you know the exact amount. If you already know your number and want fixed payments, run it through the home equity loan calculator and compare it side by side. Both are secured by your home, so missed payments can lead to foreclosure. Use the calculator to compare the interest-only and amortized scenarios before deciding which structure fits.

How to use this HELOC calculator

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

1. Home value: enter your home's current market value - a recent appraisal, the lender's automated valuation, or a conservative estimate of what it would sell for today.
2. Current mortgage balance: the amount you still owe on your first mortgage (and any existing second lien). The calculator subtracts this from your CLTV limit to find available credit.
3. Max CLTV: the highest combined loan-to-value your lender allows, commonly 80%-90%. If you are unsure, 85% is a reasonable middle-ground placeholder.
4. Amount to draw, rate & term: enter how much you plan to borrow, the quoted interest rate, and the repayment term. The calculator then shows the interest-only draw payment and the amortized repayment payment.

The result updates instantly. Read your available credit and combined LTV after the draw at the top, then compare the interest-only and repayment payments so the future "payment shock" is no surprise.

Who this calculator is for

This tool is built for homeowners weighing whether to tap their equity and how much it will really cost each month. That includes:

• Renovators funding a kitchen, addition, or multi-stage remodel where costs arrive in waves rather than all at once.
• Debt consolidators comparing a secured HELOC rate against higher-rate credit cards - while understanding the home becomes collateral.
• Buyers bridging a gap who need short-term cash and want to keep a low first-mortgage rate intact instead of refinancing.
• Investors and small-business owners using home equity as a flexible, lower-cost source of capital.
• Anyone budgeting who wants to see both the cheap draw-period payment and the larger repayment-period payment before signing.

A second worked example: smaller home, 80% CLTV

Suppose your home is worth $300,000 and you owe $180,000 on the mortgage. If your lender caps the line at an 80% CLTV, the most you can owe against the home is $240,000; subtract the $180,000 first mortgage and your available credit is $60,000. Draw $30,000 at a 9% rate and the interest-only payment during the draw period is about $225 per month ($30,000 × 9% ÷ 12). Your combined LTV after the draw is ($180,000 + $30,000) ÷ $300,000 = 70%, comfortably under the 80% cap. When the line converts to a 15-year repayment, the amortized payment climbs to roughly $304 per month - a clear illustration of how much the repayment period adds even when you have only drawn half your line.

What changes the result the most

If you adjust the inputs and watch the numbers move, a few factors dominate:

• Equity (home value minus mortgage balance): the single biggest driver of how large a line you qualify for.
• Max CLTV: the difference between an 80% and a 90% cap can be tens of thousands of dollars of available credit on the same home.
• Interest rate: because most HELOCs are variable, each 1% of rate changes your interest-only payment by about $8 per month for every $10,000 drawn.
• Amount drawn: you pay interest only on what you actually borrow, so a smaller draw means a smaller payment and a lower combined LTV.
• Repayment term: a longer term lowers the monthly repayment payment but increases total interest paid.

Key HELOC terms explained

• Equity: the part of your home you own outright - current market value minus everything you owe against it.
• CLTV (combined loan-to-value): all loans secured by the home divided by its value. Lenders cap the CLTV they will allow on a HELOC.
• Draw period: the early phase (often 5-10 years) when you can borrow and re-borrow, usually paying interest only.
• Repayment period: the later phase (often 10-20 years) when the balance amortizes into principal-and-interest payments and you can no longer draw.
• Index and margin: a variable HELOC rate equals a public index (such as the prime rate) plus a fixed margin the lender sets based on your credit and CLTV.
• Fixed-rate conversion: an option some lenders offer to lock part of your balance at a fixed rate, trading flexibility for payment certainty.

Tips to get a better line and rate

• Build equity first: a lower starting CLTV reduces the lender's risk and often earns a smaller margin over the index.
• Strengthen your credit: a higher score and a debt-to-income ratio under the lender's cap (commonly 43%-50%) widen your options - check yours with the debt-to-income calculator before you apply.
• Shop several lenders: margins, caps, and fees differ, so compare the all-in cost - not just the headline introductory rate.
• Read the fee schedule: watch for annual fees, inactivity fees, and early-closure fees that can offset a slightly lower rate.
• Draw in stages: only borrow what you need when you need it to keep interest costs and your combined LTV low.

Limitations and assumptions

This calculator is a planning estimate, not a credit offer. Keep these assumptions in mind:

• It uses a single fixed rate for illustration; a real HELOC rate is usually variable and can rise or fall over time.
• It does not include closing costs, annual fees, inactivity fees, or early-closure fees some lenders charge.
• It assumes the lender's stated max CLTV applies to your situation; actual overlays can be stricter for higher loan amounts, second homes, or investment properties.
• It does not model minimum-draw requirements or interest-only-to-amortizing transition rules that vary by lender.
• Your actual line, rate, and approval depend on your credit, income, the appraised value, and current market conditions - get a written offer before relying on these figures.

How it compares to related calculators

This page answers "how much can I borrow against my home, and what will it cost?" If you have a slightly different question, a sister tool fits better:

• For a fixed-rate lump sum instead of a revolving line, use the Home Equity Loan Calculator.
• To replace your entire first mortgage and pull out cash at once, use the Cash-Out Refinance Calculator.
• To check whether your debt load fits a lender's limits, use the Debt-to-Income Calculator.
• To estimate the payment on a brand-new first mortgage, use the Mortgage Calculator.

Sources

• Consumer Financial Protection Bureau (CFPB) - What is a home equity line of credit (HELOC)?
• Consumer Financial Protection Bureau (CFPB) - Mortgages and home equity borrowing basics.
• Internal Revenue Service (IRS) - Publication 936, Home Mortgage Interest Deduction.
• Federal Trade Commission (FTC) - Home Equity Loans and Home Equity Lines of Credit.