HELOC Calculator: How Much Can You Borrow? (2026 Guide)

You don't need a financial advisor to estimate your HELOC limit or monthly payment. Two formulas cover most of what you need to know before you apply.

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Formula 1: Your Maximum HELOC Amount

HELOC Limit = (Home Value × Max CLTV) − All Outstanding Mortgages

Most lenders allow up to 85% combined loan-to-value (CLTV).

Examples

The last example illustrates a common situation: if you bought recently or put down less than 20%, you may not have sufficient equity for a HELOC yet.

What CLTV Stands For

CLTV = Combined Loan-to-Value. It's all your mortgage debt (first mortgage + any second mortgage or HELOC) divided by your home's value.

If a lender allows 85% CLTV and your home is worth $500,000:

• Maximum total debt: $500,000 × 0.85 = $425,000
• If your first mortgage is $300,000, your HELOC cap is $425,000 − $300,000 = $125,000

Some credit unions go up to 90% CLTV; some lenders use 80%. The 85% figure is the most common.

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Formula 2: Monthly Interest Payment (During Draw Period)

During the HELOC draw period, most lenders require interest-only payments on your outstanding balance.

Monthly Interest = (Draw Amount × Annual Rate) ÷ 12

Payment Examples at 8.25% Rate (March 2026 Estimate)

You only pay interest on what you've drawn — not your full credit limit. If your limit is $100,000 and you've drawn $40,000, your monthly payment is $275, not $688.

How Rate Changes Affect Your Payment

HELOC rates are variable. If the Prime Rate moves, your payment moves.

Always stress test at rate + 2%. If the Fed raises rates by 2 percentage points and you have $100,000 drawn, your monthly interest goes from $688 to $854.

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Formula 3: Repayment Period Payment (After Draw Period)

After your 10-year draw period closes, you enter a 20-year repayment period. You pay principal + interest on whatever balance remains.

Monthly P+I Payment = [Balance × (Rate/12)] ÷ [1 − (1 + Rate/12)^(-240)]

That formula is complex. Here's a simplified table:

Monthly P+I During 20-Year Repayment at 8.5%

The repayment jump: If you had $100,000 drawn at 8.5% and were paying interest-only ($708/month), moving into repayment increases your payment to $868/month. Plan for this transition.

How to reduce the repayment shock:

• Pay down principal during the draw period
• Refinance at the end of the draw period into a new HELOC or home equity loan
• Coordinate the draw period end with a mortgage payoff to free up payment capacity

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HELOC vs Home Equity Loan: Total Cost Calculator

If you need $100,000 and are choosing between a HELOC and a home equity loan, here's a 10-year comparison:

Assumptions:

• Draw amount / loan amount: $100,000
• HELOC: 8.25% variable, interest-only for 10 years
• Home equity loan: 8.5% fixed, P+I for 20 years

The HELOC has lower monthly payments and less total cash out over 10 years — but you still owe the full balance at year 10. The home equity loan costs more monthly but chips away at principal.

Which wins depends on your plan for the balance. If you expect to pay it off (home sale, other income event), the HELOC saves money. If you need predictable amortization, the home equity loan is cleaner.

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Factors That Affect Your Actual HELOC Limit

The formula gives you a ceiling. Your actual approved limit may be lower based on:

1. Credit Score

Lenders use tiered pricing and limits. A 620 credit score may be approved for a HELOC, but at a lower LTV limit (75–80% vs 85%) than a 740+ borrower.

2. Debt-to-Income Ratio

Lenders calculate your DTI including the HELOC payment at full draw. If your existing debt obligations are already high, the approved limit may be reduced even if your equity is substantial.

3. Appraised Value (Not Zillow)

The lender orders an appraisal — which may come in lower than Zillow estimates. If your home appraises at $480,000 instead of the $520,000 you estimated, your available HELOC shrinks accordingly.

4. Lender Overlays

Individual lenders impose their own limits on top of standard CLTV guidelines. Some max at 80% CLTV, not 85%. Some have property-type restrictions.

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How to Increase Your HELOC Eligibility

If your current numbers don't give you the credit line you need, here's how to change them:

Pay Down Your Primary Mortgage

Every dollar of principal paid increases your available equity. Aggressively paying down your mortgage for 12–18 months can meaningfully improve your CLTV position.

Improve Your Credit Score

Moving from 680 to 720 can open up higher LTV options with more lenders. Strategies: pay down revolving balances below 30% utilization, dispute inaccuracies, don't open new accounts 90 days before applying.

Wait for Home Appreciation

In markets with strong appreciation, simply waiting 12–24 months increases your available HELOC limit without any action on your part.

Get a Fresh Appraisal

If your home has appreciated but your lender is using an older automated valuation, a full appraisal (which you can request) may support a higher value — and therefore a larger credit line.

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Common Calculation Mistakes

Using Zillow as Your Home Value

Zillow's Zestimate is a rough estimate with significant variance — sometimes 10–15% off the actual appraised value. Build in a buffer: calculate your HELOC eligibility using Zillow value minus 10%.

Forgetting a Second Mortgage

CLTV includes all mortgage debt. If you have a second mortgage or existing HELOC, that balance reduces your available new HELOC. Formula: (Home Value × 85%) − First Mortgage − Second Mortgage = Max New HELOC.

Not Accounting for Variable Rate Risk

Calculating affordability based on today's rate is a mistake. Run your monthly payment calculation at today's rate + 2% to ensure you can handle rate increases.

Calculating Interest on the Full Limit, Not the Draw

You pay interest on what you've drawn, not your credit limit. If you need $60,000 but your limit is $120,000, your payment calculation should use $60,000.

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Frequently Asked Questions

How do I know my home's current value for the calculation? Use Zillow or Redfin for a rough estimate, then reduce by 10% for a conservative calculation. For an exact figure, pay for an independent appraisal ($400–$700) before applying.

Does the bank use my asking price or appraised value? The lender orders their own appraisal and uses that value. If you paid $600,000 two years ago but the home is now worth $650,000 (appraised), they'll use $650,000. Vice versa if it's dropped.

Can I get a HELOC up to 90% LTV? Some credit unions allow 90% CLTV. Most banks and online lenders cap at 85%. Higher LTV means less equity buffer and potentially higher rates.

What if my HELOC limit calculation is negative? Your combined mortgage debt exceeds 85% of your home's value. Options: pay down the mortgage, wait for appreciation, or look into a government-backed program. A conventional HELOC isn't available at this LTV.

How much of my HELOC should I draw? Only what you need. Drawing more than you need means paying interest on idle funds. A partially-drawn HELOC is a liability; use it strategically.

Can my lender reduce my HELOC limit after I open it? Yes. During the draw period, lenders can freeze or reduce your HELOC if your home value drops significantly or your creditworthiness deteriorates. This happened to many borrowers during the 2008–2010 housing downturn.

How often does the interest rate change on a HELOC? Most HELOCs adjust monthly with the Prime Rate. When the Fed raises or lowers its target rate, your HELOC rate adjusts at your next billing cycle.

Is there a minimum draw requirement? Some lenders require a minimum initial draw (often $5,000–$10,000) at closing. Check your loan agreement — you don't want to be forced to draw more than you need.

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Use HonestCasa's HELOC calculator to get a personalized estimate based on your home's value and equity position, or apply for a HELOC to see your actual rate.