How a HELOC actually works
A home equity line of credit is a credit card secured by your house: a revolving line you can draw, repay and redraw. It runs in two phases. During the draw period (typically 10 years) you borrow as needed and the required payment is usually interest-only. Then the repayment period (10-20 years) begins: no new draws, and the balance amortizes into principal-plus-interest payments. The rate is almost always variable — prime plus a margin — so it moves with the Fed, in both directions, for the life of the line.
How big a line you can get
Lenders cap your mortgage plus the line at a combined loan-to-value (CLTV) — commonly 80-90% of appraised value. The formula is one line: home value × CLTV − mortgage balance. A $450,000 home at 85% CLTV with $280,000 owed supports up to $102,500. What the lender approves also depends on credit score (mid-600s minimum at most banks, best pricing above 740) and a debt-to-income ratio that survives the new payment — check yours with the DTI calculator, and see your raw equity position in the home equity calculator.
The payment shock, quantified
The draw-period math lulls people. Interest-only on $50,000 at 8.5% is about $354 a month. When the repayment period starts, that same balance amortizing over 20 years costs about $434 — a 23% jump. Shorter repayment periods bite harder: over 15 years it's $492 (+39%), over 10 years $620 (+75%). And that assumes rates sat still for a decade, which variable rates don't. The classic HELOC casualty borrowed to the limit, paid the minimum for ten years, built zero principal, and met a 50%+ payment jump — this calculator's whole job is making that visible up front.
HELOC vs the alternatives
- Home equity loan: same collateral, but a fixed lump sum at a fixed rate with level payments from day one. Better when the cost is known and one-time (a roof, a settled renovation bid). The HELOC wins for staged or uncertain costs — you pay interest only on what's drawn.
- Cash-out refinance: replaces the whole first mortgage. Made sense when rates were falling; with a 3% mortgage in hand and 6-7% refi rates, surrendering the old rate to touch equity is usually a bad trade — the HELOC leaves the first mortgage untouched.
- Personal loan: unsecured, so pricier (10-15%+) — but your house isn't collateral. For smaller amounts on shorter timelines, compare with the loan comparison calculator; the rate gap shrinks fast after fees.
What a HELOC is good for — and not
The strong use cases share a trait: the money buys something durable or bridges a gap you can see across. Staged renovations that add value, a bridge between buying one house and selling another, an emergency backstop opened before it's needed (a $0-balance line costs little or nothing to keep open). The weak cases: consolidating card debt without fixing the spending that built it — the consolidation math can look great right up until the cards refill and the debt is now attached to your house — and funding lifestyle spending on vacations or cars, which converts depreciating consumption into a lien on your home. The deduction rules follow the same logic: HELOC interest is only tax-deductible when the money buys, builds or substantially improves the home securing it.
Costs and fine print worth reading
- Rate structure: your rate is prime + margin. The margin is negotiable and score-dependent; intro teaser rates often expire after 6-12 months.
- Floors and caps: most HELOCs have a lifetime cap (often 18%) and a floor below which the rate won't drop, whatever prime does.
- Fees: annual fees ($50-100), early-closure fees if you close within 2-3 years, and sometimes appraisal/origination costs — many lenders waive them; ask.
- Freeze risk: the lender can freeze or reduce the line if home values fall or your credit deteriorates — 2008's unpleasant surprise. An unused HELOC is a good backstop but shouldn't be your only emergency plan; size a cash cushion with the emergency fund calculator.
- Fixed-rate locks: many lenders let you convert chunks of the drawn balance to a fixed rate — useful hedge once a big draw is done.