HELOC calculator

HELOC – Home Equity Loan Calculator

The payment jump nobody warns you about

A HELOC works in two distinct phases, and the gap between them catches people off guard more than almost anything else in home lending. During the draw period — typically 10 years — most HELOCs only require interest-only payments. That $40,000 draw at 9% might cost you just $300 a month, which feels genuinely manageable. Then the draw period ends, the repayment period starts, and suddenly you owe principal and interest on the full balance, often over a shorter window than a typical mortgage. That same $40,000 can jump from $300 a month to well over $350 or $400, sometimes more, depending on the repayment term and rate at the time.

None of this is hidden exactly — it’s in the loan documents — but interest-only payments during the draw period can create a false sense of what the loan actually costs long-term. This calculator shows both numbers side by side specifically so that surprise doesn’t happen after you’ve already committed.

Why the rate matters more here than on almost any other loan

Fixed-rate mortgages lock in a number and it stays put. HELOCs are usually variable, tied to a benchmark rate that moves with broader interest rate conditions. Borrow at a low rate today, and there’s a real chance your payment looks different in three years — for better or worse. If you’re using a HELOC for something with a long payoff horizon, it’s worth asking your lender whether a fixed-rate conversion option exists for some or all of the balance, since some lenders offer this and it can meaningfully reduce the uncertainty.

What “combined loan-to-value” actually means

Lenders don’t just look at your home’s value in isolation — they look at your total debt against that value, meaning your existing mortgage plus the new HELOC combined. An 80% max CLTV on a $450,000 home with a $250,000 mortgage doesn’t mean you can borrow up to 80% of $450,000 fresh; it means your mortgage and HELOC together can’t exceed $360,000, which in this example leaves $110,000 in available credit. This is a common point of confusion, and it’s exactly why the “maximum available” figure this calculator gives you already accounts for your existing mortgage balance rather than ignoring it.

A word on what a HELOC actually secures

A HELOC is secured by your home, the same as your primary mortgage. That’s part of why the rates tend to be lower than unsecured options like personal loans or credit cards — but it also means missed payments carry real consequences, up to and including foreclosure risk in a worst-case scenario. Borrowing against home equity for something with a clear return (a renovation that adds value, consolidating higher-interest debt) is a different risk profile than borrowing against it for ongoing expenses that don’t build anything back.

Can I pay down the balance during the draw period even though it’s interest-only? Yes, typically — most HELOCs allow (and don’t penalize) paying more than the interest-only minimum during the draw period, which reduces both your balance and the eventual repayment-period payment.

What happens if I don’t draw the full available amount? Nothing bad — a HELOC is a line of credit, not a lump-sum loan, so you generally only pay interest on what you actually draw, not on your full approved limit.