HELOC Calculator

Field guide

What is a HELOC and how does it work?

A home equity line of credit (HELOC) is a revolving credit line secured by the equity in your home. Unlike a traditional home equity loan, which delivers a single lump sum, a HELOC works more like a credit card: you can borrow, repay, and borrow again up to your approved credit limit throughout the draw period. Because the debt is backed by real property, lenders can offer significantly lower rates than unsecured personal loans or credit cards.

HELOCs are popular for home renovations, debt consolidation, college tuition, and emergency reserves. Their flexibility is their main advantage - you only pay interest on what you actually borrow, not on the full credit line sitting unused in your account.

How the credit limit is calculated

Lenders use a metric called the combined loan-to-value (CLTV) ratio to set the maximum they will lend. The formula is straightforward:

For example, if your home is worth $400,000, your lender allows 85% CLTV, and your remaining mortgage balance is $250,000:

Most lenders cap CLTV at 80-85%, though some go up to 90% for well-qualified borrowers. The lower your existing mortgage balance relative to your home value, the larger the credit line you can access.

The draw period

The draw period is the first phase of a HELOC, typically lasting 5 to 10 years. During this time you can access funds freely up to your credit limit. The minimum monthly payment due is interest-only on the outstanding balance:

Because you only pay interest on the amount drawn - not on the total credit line - your payment stays modest if you borrow conservatively. You can also make voluntary principal payments during the draw period, which reduces your outstanding balance and the interest accruing on it.

One nuance worth understanding: the interest rate on most HELOCs is variable, typically tied to the prime rate plus a margin. This means your monthly payment can rise or fall as rates move. Run this calculator with a higher rate scenario to stress-test your budget.

The repayment period

When the draw period ends, the line closes to new borrowing and your outstanding balance converts to a fully amortizing installment loan. You repay principal and interest in fixed monthly installments over the repayment term, commonly 10 to 20 years:

Where P is the outstanding balance at the end of the draw period, r is the monthly interest rate (APR divided by 12), and n is the number of repayment months.

This payment is almost always substantially higher than the interest-only draw payment, which surprises many borrowers who have not planned for the transition. For a $60,000 balance at 8.5% APR repaid over 20 years, the monthly payment jumps from $425 (draw, interest-only) to about $521 (repayment, P+I). That 23% increase can strain a budget that was built around the draw-period minimum.

How to use this calculator

• Home value - use a current market estimate, not your purchase price. Sites like Zillow or Redfin provide rough estimates, but a formal appraisal gives the most accurate figure.
• Mortgage balance - enter the payoff balance on your first mortgage. This is not the same as your remaining principal schedule amount; call your servicer or check your last statement for the precise figure.
• Max LTV - select the CLTV tier your lender offers. 80% and 85% are the most common. Higher LTV means more credit available but less equity cushion.
• Amount to draw - enter what you actually plan to borrow. This number drives the payment calculations. If you plan to draw gradually, use your expected peak balance.
• Interest rate - use your lender's current quoted rate. Because most HELOCs are variable, run the calculator at 2-3% higher to see a stress-test scenario.
• Draw and repayment periods - match these to your loan terms. If you have not yet applied, 10 years draw and 20 years repayment is the most common structure.

Key risks to understand before borrowing

• Payment shock. The jump from interest-only to full P+I payments is the biggest trap for HELOC borrowers. Build a repayment-period budget before you draw, not after.
• Rate variability. A 2% rate increase on a $75,000 balance adds $125 per month to your draw payment. Large balances at the end of long draw periods can carry significant rate risk.
• Your home is the collateral. Failure to repay a HELOC can result in foreclosure. Only borrow amounts you are confident you can repay even if your income or the rate environment changes.
• Falling home values. If your home value drops, your equity shrinks. Lenders can reduce or freeze your credit line if they determine the collateral no longer supports it.
• Closing costs. HELOC origination fees typically run from $200 to $2,000 or more. Some lenders absorb these costs in exchange for a small rate premium; others pass them through directly.

Tax deductibility

Under current U.S. tax law, HELOC interest is deductible on federal returns only when the funds are used to buy, build, or substantially improve the home securing the line. Interest on draws used for other purposes - debt consolidation, vacations, tuition - is generally not deductible. State rules vary. Always consult a qualified tax advisor before assuming deductibility.

HELOC vs. home equity loan

A home equity loan gives you a lump sum at a fixed rate, with fixed monthly payments from day one. A HELOC gives you flexible access to funds with variable payments. The right choice depends on how predictable your borrowing needs are. If you know the exact amount you need and want rate certainty, a home equity loan is simpler. If you need ongoing access over several years, a HELOC is usually the more cost-effective structure.

Disclaimer

This calculator is provided for educational and planning purposes. It assumes a constant interest rate across both periods and does not reflect closing costs, origination fees, or rate adjustments. Actual HELOC terms vary by lender, state, and borrower qualification. Consult a licensed mortgage professional or financial advisor before making any borrowing decision.