HELOC Calculator (Credit Line & Interest-Only Payment)
Enter your home's value, what you still owe, and a combined LTV cap to see the equity you could borrow against and the credit line a lender might extend. Add a rate to preview the interest-only payment during the draw period.
A realistic current market value, not your purchase price
What you still owe on the home, all liens combined
Mortgage plus HELOC as a share of value; many lenders cap near 80%
Usually variable; check a current quote for your credit profile
Available equity
$170,000
home value minus the $280,000 you owe
Potential credit line
$80,000
at 80% combined LTV; you're at 62% today
Interest-only payment
$567
per month if you drew the full line at 8.5%
Where your home value sits
- Mortgage balance$280,00062%
- Potential credit line$80,00018%
- Equity buffer you keep$90,00020%
Estimates only. Lenders also weigh credit score, income, and debt-to-income ratio, and the payment shown is the interest-only minimum during the draw period, not what repayment eventually costs.
The line-size formula lenders use
A HELOC is a revolving credit line secured by your home, and its size comes from one equation: home value times the lender's maximum combined loan-to-value, minus your current mortgage balance. The "combined" part matters because the cap covers every loan against the house at once. Take a $450,000 home with $280,000 still owed. Total equity is $170,000, but at an 80% CLTV cap the lender's ceiling is $360,000, so the line tops out at $80,000. Draw the full amount at 8.5% and the interest-only payment is about $567 a month. The remaining $90,000 of equity stays untouchable by design: it's the cushion that protects both sides if prices fall.
Draw period, then repayment period
A HELOC lives in two phases. During the draw period, commonly around ten years, it behaves like a credit card with your house as collateral: borrow, repay, borrow again, with interest-only minimum payments on what's outstanding. Then the switch flips. In the repayment period, borrowing stops and the balance amortizes over the remaining term with principal and interest due every month. Because rates are usually variable and the interest-only floor makes the early years feel cheap, the payment jump at the handoff surprises many borrowers. The honest way to plan is to size the payment on the full amortizing cost, not the minimum, and to check the fit against your debt-to-income ratio the way a lender will.
When tapping equity earns its keep
Home equity is often a household's largest asset, and a line against it is cheaper than almost any unsecured borrowing because the bank holds excellent collateral: your home, which is also why the stakes are higher. Renovations that add value, bridging an irregular income year, or replacing costlier debt can all justify it. Funding routine spending usually can't, and a HELOC is not a substitute for an emergency fund, since lenders can freeze lines exactly when times get hard. Before borrowing, know where the equity sits in your bigger picture: the net worth calculator puts your home, mortgage, and everything else on one page.
Frequently asked questions
How is a HELOC credit line calculated?
Lenders multiply your home's value by a maximum combined loan-to-value ratio, often around 80%, then subtract your current mortgage balance. On a $450,000 home with $280,000 owed, 80% of value is $360,000, leaving up to $80,000 of line. Your credit score, income, and existing debts can shrink that further.
What is combined loan-to-value (CLTV)?
All debt secured by the home, your mortgage plus the full HELOC limit, divided by the home's value. Lenders cap CLTV so a price dip doesn't leave the loans worth more than the house. A tighter cap means a smaller line but also a bigger safety buffer for you.
What happens when the draw period ends?
The line freezes and repayment begins: you can no longer borrow, and payments switch from interest-only minimums to principal plus interest on whatever you owe. That jump can be steep. A $50,000 balance that cost a few hundred dollars a month in interest suddenly amortizes over 10-20 years at a variable rate.
Is HELOC interest tax-deductible?
Sometimes. Interest can be deductible when the money is used to buy, build, or substantially improve the home securing the line, subject to limits that change with tax law. Borrowing for other purposes generally isn't deductible. Check current IRS guidance or a tax professional before counting on it.
What's the difference between a HELOC and a home equity loan?
A HELOC is a revolving line you draw as needed, usually at a variable rate, and you pay interest only on what you use. A home equity loan hands you a lump sum at a fixed rate with a fixed payment from day one. Lines suit ongoing projects; lump sums suit one-time known costs.
Does this calculator save my numbers?
No. Everything runs in your browser and nothing you type is stored or sent anywhere.
Want this to update itself?
Stoia connects your real accounts and keeps the full picture current: net worth, budgets, and goals. Launching in 2026.