HELOC Calculator

How It Works

A HELOC Calculator helps you determine how much equity you can borrow against your home and estimates your monthly payments based on different repayment strategies. This is essential for homeowners considering a home equity line of credit as a way to access funds for major expenses, renovations, or debt consolidation. This tool is designed for both quick estimates and detailed planning scenarios. Results update instantly as you adjust inputs, making it easy to compare different approaches and understand how each variable affects the outcome. For best accuracy, use precise measurements rather than rough estimates, and consider running multiple scenarios to establish a realistic range of expected results.

The Formula

Variables

• Home Value — The current fair market value of your home, typically estimated using recent appraisals, comparable sales (comps), or online valuation tools like Zillow or your property tax assessment
• Current Mortgage Balance — The remaining principal you owe on your primary mortgage, which can be found on your latest mortgage statement or online lender portal
• Combined LTV Limit — The loan-to-value percentage that your lender allows—typically 80% to 90%—representing the maximum percentage of your home's value you can borrow against (first mortgage plus HELOC combined)
• HELOC Interest Rate — The variable or fixed annual interest rate your lender charges on borrowed funds; HELOC rates are typically prime-based and fluctuate with market conditions, currently ranging from 5% to 10%+
• Amount to Draw — The specific amount of money you plan to borrow from your available HELOC credit line during the draw period (typically the first 5-10 years)

Worked Example

Let's say you own a home valued at $400,000 with a current mortgage balance of $200,000. Your lender offers a combined LTV limit of 85% and a HELOC interest rate of 8.5% annually. First, calculate your maximum borrowing power: $400,000 × 0.85 = $340,000 total available, minus your $200,000 mortgage = $140,000 available home equity and maximum HELOC credit line. If you decide to draw $50,000 from this line, your interest-only monthly payment would be ($50,000 × 0.085) / 12 = $354.17 per month. However, if you want to repay over 20 years instead, your monthly payment would be approximately $479—higher because you're paying down principal, not just interest. This illustrates why interest-only payments appear attractive but rebuild equity more slowly.

Practical Tips

• Check your home value realistically—use recent comparable sales in your area, not estimates from years ago. An overstated home value won't increase your actual borrowing power, and lenders will order their own appraisal anyway.
• Understand your combined LTV: if your lender limits you to 85% combined LTV, that includes both your mortgage and HELOC. A $300,000 home at 85% LTV means only $255,000 total debt (mortgage + HELOC) is allowed.
• Interest-only payments during the draw period (typically 5-10 years) are tempting but trap you in a cycle of never building equity—plan to switch to a repayment schedule well before the draw period ends to avoid payment shock.
• Lock in a fixed rate if you expect interest rates to rise, especially if you plan to keep the HELOC open for many years. Variable rates can save you money initially but expose you to higher costs when the Fed raises rates.
• Factor in closing costs (typically $500-$2,500) and potential appraisal fees when deciding whether to open a HELOC—a small draw might not justify the upfront expenses unless you expect future uses.

Last updated: April 02, 2026 · Reviewed by the CalcSuite Editorial Team · About our methodology