How This Calculator Works

A Home Equity Line of Credit (HELOC) is a revolving credit line secured by your home's equity. It works like a credit card with a much lower rate and your house on the line: you're approved for a maximum credit limit, draw against it as needed during a "draw period" (typically 5–10 years), then pay it back during a "repayment period" (typically 10–20 years).

The calculator runs three layered computations. First, it estimates your maximum HELOC line size:

Max HELOC = (Home value × Max LTV %) − Mortgage balance

Most lenders cap combined loan-to-value (CLTV) at 80–90% of the home's appraised value. The CLTV is your existing mortgage plus the new HELOC, divided by home value. A home worth $450,000 with a $200,000 mortgage and an 85% max CLTV supports a HELOC of up to $182,500 — calculated as (450,000 × 0.85) − 200,000.

Second, your interest-only payment during the draw period is simply the drawn balance times the monthly rate: draw × (APR ÷ 12). This is the small payment that makes HELOCs feel cheap during the first few years.

Third, your amortizing payment during the repayment period uses the standard mortgage formula on whatever balance remains when the draw period ends. The "total cost if fully drawn" output sums the interest-only payments across the entire draw period plus all amortized payments across the repayment period — the realistic total cost of using the full line.

Understanding Your Results

Five numbers worth knowing how to read:

Maximum HELOC available — the credit line a typical lender would approve at the LTV you specified. You can usually draw any amount up to this cap during the draw period.
Available equity — your home's value minus what you still owe on the mortgage. The HELOC max is always smaller than this because lenders won't lend against 100% of equity.
Current LTV — what percentage of your home's value the existing mortgage represents. If this is already above your max LTV, you don't have HELOC capacity yet.
Interest-only / month — the payment during the draw period, calculated on the drawn balance only. This is what your monthly cash flow looks like for the first 5–10 years.
Repayment P&I / month — the payment after the draw period closes, calculated on the remaining balance amortized over the repayment term. This is often 2–3× the interest-only payment and is the source of "payment shock" complaints from HELOC borrowers who didn't plan for it.

The total-cost-if-fully-drawn output is the most honest number on this page. A $50,000 draw at 8.5% with a 10-year interest-only draw and 15-year repayment costs over $90,000 in cumulative payments — almost double the drawn amount. If you're using a HELOC to fund something with no expected return (luxury renovation, vacation, debt consolidation that doesn't reduce overall debt), that's the price you're paying for the convenience of revolving credit.

Factors That Affect Your HELOC

Variable rate exposure

HELOCs almost always carry a variable rate tied to the Wall Street Journal prime rate, with a margin (typically prime + 0% to prime + 2%). When the Fed moves, your rate moves — usually within one billing cycle. A HELOC that opens at 8.5% can be at 11% two years later if rates rise, and your interest-only payment scales proportionally. Read the rate cap (the maximum lifetime rate, often 18%) before drawing meaningfully.

Combined loan-to-value (CLTV) limits

Most banks cap CLTV at 80–90%. Credit unions sometimes go higher. The lower your CLTV, the better the rate and terms; lenders price aggressively for low-risk lines. If you're at 50% CLTV, you'll see the cleanest pricing; at 90%, you'll see rate add-ons of 0.5–1.5%.

Credit score

HELOC pricing is heavily score-dependent. Lenders typically tier at 740/720/700/680. Below 680, lines are still available but at meaningfully higher margins, lower max CLTVs, and often a draw-period restriction (5 years instead of 10).

Documentation: full-doc vs HELOC streamline

Most HELOCs require income verification, employment verification, and an appraisal — same as a mortgage origination. Some lenders offer "streamline" HELOCs that use an automated valuation model (AVM) instead of an appraisal, which is faster (1–2 weeks vs 30–45 days) but caps line size lower.

Draw period vs repayment period mechanics

During the draw period, you can borrow, repay, and re-borrow against the line. After it closes, the line is locked at whatever balance you held and starts amortizing. Some lenders allow you to convert the drawn balance to a fixed-rate term loan at any time during the draw period — useful if rates are rising and you want to lock in.

Tax deductibility

Post-TCJA, HELOC interest is only deductible if the proceeds are used to "buy, build, or substantially improve" the home that secures the loan. Using a HELOC for a kitchen remodel: deductible. Using it for a car or college tuition: not deductible. Track the use carefully if you plan to claim it.

Annual fees and inactivity fees

Many HELOCs carry a $50–$100 annual fee and an "inactivity fee" if you don't draw at least once per year. Some lenders waive these in the first year as a teaser. Cancellation fees (often $250–$500) can apply if you close the line within 3 years of opening. Always ask about these upfront.

HELOC vs cash-out refinance

If you need a one-time lump sum and rates are favorable, a cash-out refinance often beats a HELOC because the rate is fixed and typically lower. HELOCs win when you need flexibility — a series of unknown draws over years (renovation phases, emergency reserve, college expenses), or as a low-cost standby line you may never use.

Frequently Asked Questions

How long does a HELOC take to open?

Full-doc HELOCs typically take 30–45 days from application to funding (similar to a refinance). Streamline HELOCs using an AVM can close in 7–14 days but usually cap line size lower. The slowest steps are the appraisal and title search; you can speed things up by providing recent property tax bills and homeowners insurance declarations upfront.

Does a HELOC affect my credit score?

The hard inquiry at application costs a few points temporarily. Once open, the HELOC reports as revolving credit, which can help your credit mix. The bigger risk is utilization — drawing 50%+ of the line can drop your score by 20–40 points because credit bureaus treat HELOCs like high-balance credit cards. Keep utilization below 30% if you can.

What happens at the end of the draw period?

The line "closes" — you can no longer borrow new funds — and the outstanding balance enters the repayment period. Payments jump from interest-only to fully amortizing P&I, often 2–3× the previous payment. Some lenders offer a "draw period extension" or conversion to a fixed-rate loan at this point. Plan ahead; "payment shock" at the end of the draw period is a leading cause of HELOC default.

Can my lender freeze or reduce my line?

Yes. HELOC agreements typically reserve the lender's right to freeze or reduce the line if your home's value drops, your credit score falls, or your income changes materially. This happened widely in 2008–2010 and again briefly in 2020. Drawn balances are protected (you keep the money you've already borrowed), but undrawn capacity can disappear.

Is the interest tax-deductible?

Only if the proceeds are used to buy, build, or substantially improve the home that secures the loan, and only up to the $750,000 acquisition-debt cap (combined with your first mortgage). Using a HELOC for a kitchen renovation: deductible. Using it for a car, vacation, or credit-card payoff: not deductible. Keep receipts.

What's the difference between a HELOC and a home equity loan?

A home equity loan is a one-time lump-sum disbursement at a fixed rate with fixed monthly payments from day one — like a second mortgage. A HELOC is revolving credit you draw from as needed at a variable rate, with interest-only payments during the draw period. Home equity loans are simpler and more predictable; HELOCs are more flexible.

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Next Steps

Once you have your line size and payment estimates, the next steps depend on what you're financing:

Refinance Calculator — compare against a cash-out refinance for one-time needs.
Home Value Estimator — get a more precise home value (lenders will use their own appraisal but knowing your ballpark helps).
Renovation ROI Calculator — if you're using the HELOC for a project, model the resale impact first.
Types of Mortgages — for context on how HELOCs compare to other home financing.

HELOC Calculator

Equity & line details