A home equity line of credit (HELOC) lets you borrow against the value you've built up in your home, typically at rates far below credit cards or personal loans. This HELOC calculator answers the two questions that matter before you apply: how much credit a lender is likely to extend, and what it will actually cost per month. Enter your home's value, your remaining mortgage balance, and the lender's maximum combined loan-to-value (LTV) ratio — usually 80% to 85% — and the calculator shows your available credit line instantly, along with the interest-only payment during the draw period and the fully amortizing payment once repayment begins.
HELOC Calculator
Finance
How much home equity credit you can borrow and what it costs
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Why HELOC Calculator Matters
The two-phase structure of a HELOC surprises many borrowers: during the draw period (often 10 years) you may pay interest only, and the payment can then jump sharply when principal repayment starts. On a $100,000 draw at 8.5%, interest-only is about $708/month — but the 20-year repayment payment is roughly $868, and if rates rise (HELOCs are usually variable), both go up. Seeing the full picture before borrowing prevents the payment-shock scenario that gets homeowners into trouble, and the equity chart clarifies exactly how much cushion remains in your home.
The HELOC Calculator Formula, Explained
Available credit = (Home value × Max LTV%) − Mortgage balanceLenders cap total borrowing against the home (existing mortgage plus HELOC) at the LTV limit. If your home is worth $500,000 and the lender allows 80% combined LTV, total debt can reach $400,000; subtracting a $280,000 mortgage leaves a $120,000 potential credit line. The interest-only payment is simply the drawn amount × annual rate ÷ 12, and the repayment-phase payment uses the standard amortization formula over the repayment term.
How to Use the HELOC Calculator: Step by Step
Enter your home's current market value
Enter your home's current market value — a recent appraisal or a realistic estimate from comparable sales.
Enter your remaining mortgage balance from your latest state
Enter your remaining mortgage balance from your latest statement.
Set the maximum combined LTV your lender allows (80% is the
Set the maximum combined LTV your lender allows (80% is the common default; some go to 85% or 90%).
Enter the HELOC interest rate you've been quoted
Enter the HELOC interest rate you've been quoted — remember most HELOCs are variable.
Optionally set a planned draw amount and repayment period un
Optionally set a planned draw amount and repayment period under Advanced options; the draw defaults to your full available credit.
Review your available credit, both monthly payments, and the
Review your available credit, both monthly payments, and the equity-position chart.
HELOC Calculator Examples: Real-World Scenarios
1
Typical 80% LTV line
Home worth $500,000, mortgage balance $280,000, lender allows 80% combined LTV.
Home value:$500,000
Mortgage balance:$280,000
Max LTV:80%
Calculation
Maximum total debt = $500,000 × 80% = $400,000. Subtracting the $280,000 mortgage leaves $120,000 of available HELOC credit — even though total equity is $220,000, the lender keeps a 20% buffer.
Result
$120,000 available credit line
2
Payment on a $100,000 draw
Drawing $100,000 at 8.5% with a 20-year repayment period.
Draw amount:$100,000
Rate:8.5%
Repayment period:20 years
Calculation
Interest-only payment = $100,000 × 8.5% ÷ 12 ≈ $708/month during the draw period. Once repayment begins, the amortizing payment over 240 months is about $868/month — a built-in $160 jump before any rate changes.
Result
$708/mo interest-only → ≈ $868/mo in repayment
3
Thin equity
Home worth $350,000, mortgage balance $295,000, 80% LTV limit.
Home value:$350,000
Mortgage balance:$295,000
Max LTV:80% vs 90%
Calculation
Maximum debt = $280,000, which is below the existing mortgage — available credit is $0. The owner would need the home to appreciate, the balance to fall, or a lender allowing 90% LTV (which would yield $315,000 − $295,000 = $20,000).
Result
$0 at 80% LTV; $20,000 at 90%
Common Mistakes to Avoid
- Confusing total equity with borrowable equity — the lender's LTV cap always reserves a buffer.
- Budgeting around the interest-only payment and being unprepared when the repayment phase roughly doubles it on long draws.
- Forgetting HELOC rates are variable: a 2-point rate rise on $100,000 adds about $167/month in interest alone.
- Using a HELOC for consumption rather than value-adding purposes (renovation, debt consolidation at lower rates, emergencies).
- Ignoring closing costs, annual fees, and early-closure fees when comparing offers.
Tips & Tricks
- Interest on a HELOC is generally only tax-deductible in the U.S. when the funds buy, build, or substantially improve the home securing it — confirm with a tax professional.
- Paying principal during the draw period, even voluntarily, shrinks the repayment-phase shock dramatically.
- Compare a HELOC against a fixed-rate home equity loan if you need one lump sum and want payment certainty.
- Get quotes from at least three lenders — margin over the prime rate varies widely.
- Keep combined LTV below 80% where possible; it usually earns better pricing and preserves an equity cushion against price declines.
A HELOC is cheap, flexible credit — with a variable rate and a delayed payment jump baked in. Know your real available credit, stress-test the repayment-phase payment at a higher rate, and the product becomes a tool rather than a trap.
HELOC Calculator — Frequently Asked Questions
Related Calculators
Authoritative References
CFPB — What is a HELOC?
consumerfinance.gov — Authoritative reference
Federal Reserve — home equity lines of credit guide
federalreserve.gov — Authoritative reference
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