How this calculator works
Maximum line: home value × the lender’s maximum combined loan-to-value (often 80% to 90%), minus your mortgage balance.
During the draw period, usually 10 years, many HELOCs require interest only: balance × rate ÷ 12.
In the repayment period, usually 10 to 20 years, the balance is paid off with principal and interest, so the payment rises, sometimes sharply.
HELOC rates are usually variable (prime rate plus a margin), so the payments shown change if rates move.
Worked example
$450,000 home, $250,000 mortgage, 85% CLTV, $50,000 drawn at 8%
- Maximum line: $450,000 × 85% − $250,000 = $132,500.
- Interest-only payment: $50,000 × 8% ÷ 12 = $333.33.
- Repayment over 20 years: $418.22 a month, about $85 more.
Questions people ask
Is HELOC interest tax deductible?
Only if you itemize and the money is used to buy, build or substantially improve the home securing the loan, within the overall mortgage debt limits.
HELOC or home equity loan?
A HELOC is a flexible, usually variable-rate line you draw as needed; a home equity loan is a lump sum at a fixed rate with fixed payments.
What happens if home values fall?
Lenders can freeze or reduce an unused line if your equity drops, so don’t rely on it as your only emergency fund.
What are the risks?
Your home secures the line, so missed payments can lead to foreclosure. Plan for the higher repayment-period payment from the start.
Last reviewed October 2, 2026