A Home Equity Line of Credit (HELOC) is a revolving line secured by your home. Many HELOCs have an interest‑only draw period followed by an amortized repayment period.

How is maximum HELOC size estimated?

Many lenders cap the combined loan‑to‑value (CLTV). Max line ≈ CLTV_limit × Home Value − Current Mortgage Balance.

Are payments during the draw period interest‑only?

Often yes, which keeps the principal roughly unchanged until repayment starts. Your agreement may allow or require principal payments.

Does the calculator include fees and taxes?

No. It excludes closing costs, annual fees, rate caps, and taxes. Always check lender disclosures.

Most HELOCs have variable rates. You can model different draw and repayment rates separately in this tool.

What if my draw exceeds the max line?

The tool will warn you and mark the scenario as infeasible. Reduce the draw or increase the CLTV limit if your lender allows it.

HELOC Calculator

This professional HELOC calculator helps homeowners and advisors estimate maximum line size, combined loan-to-value (CLTV), interest-only draw payments, amortized repayment payments, and total interest. It is designed for quick planning, lender prequalification checks, and side-by-side scenario analysis.

Enter Your Details

Home value

Current mortgage balance

Max combined LTV (CLTV)

Desired initial draw

Draw period (years)

Repayment term (years)

APR during draw

APR during repayment Same as draw

All fields marked with * are required. Validation happens as you leave each field and on calculate.

Results

Maximum HELOC line $0.00

CLTV after draw 0.00%

Draw payment (interest-only) $0.00

Repayment payment (amortized) $0.00

Total interest (draw + repayment) $0.00

Feasibility Awaiting inputs

Assumes a single lump-sum draw at the start of the draw period, interest-only during draw, and full amortization during repayment. Taxes, fees, and caps not included.

Data Source and Methodology

Authoritative Data Source: OpenStax (2016), Algebra and Trigonometry — Section 6.8 “The Mathematics of Finance” (Amortization formula). Available at: openstax.org/books/algebra-and-trigonometry/pages/6-8-the-mathematics-of-finance. All payment and total interest calculations follow the standard amortization and simple interest formulas presented therein. For regulatory and product context on HELOCs, see CFPB: What is a HELOC and how does it work?.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

Maximum line: $ L_{\max} = \max\!\big(0,\ \text{CLTV}_{\max}\cdot V - M \big) $

CLTV after draw: $ \text{CLTV}_{\text{after}} = \dfrac{M + D}{V} $

Interest-only payment during draw: $ I_{\text{draw, m}} = D \cdot \dfrac{r_d}{12} $

Amortized repayment payment: $ P = \dfrac{r_r/12 \cdot B}{1 - (1 + r_r/12)^{-n}} $, with $ B = D $ at repayment start

Total interest: $ I_{\text{total}} = I_{\text{draw, m}} \cdot n_d + (P \cdot n_r - B) $

Glossary of Variables

V — Home value (USD)
M — Current mortgage balance (USD)
CLTV_max — Lender’s maximum combined loan-to-value (decimal, e.g., 0.85)
L_max — Estimated maximum HELOC line (USD)
D — Desired initial draw (USD)
r_d — Annual Percentage Rate during draw (decimal, e.g., 0.0825)
r_r — Annual Percentage Rate during repayment (decimal)
n_d — Draw period in months
n_r — Repayment period in months
I_draw,m — Monthly interest-only payment during draw (USD)
P — Monthly amortized payment in repayment (USD)
I_total — Total interest paid across draw and repayment (USD)

How It Works: A Step-by-Step Example

Suppose: V = $500,000; M = $300,000; CLTV_max = 85%; D = $50,000; r_d = 8.25%; draw period = 10 years; r_r = 8.25%; repayment = 20 years.

Maximum line: $ L_{\max} = 0.85\cdot 500{,}000 - 300{,}000 = 125{,}000 $ → draw of $50,000 is within limit.
CLTV after draw: $ (300{,}000 + 50{,}000)/500{,}000 = 0.70 = 70\% $.
Interest-only draw payment: $ I_{\text{draw, m}} = 50{,}000 \times 0.0825/12 \approx \$343.75 $.
Repayment payment: $ P = \dfrac{(0.0825/12)\cdot 50{,}000}{1-(1+0.0825/12)^{-240}} \approx \$427.39 $.
Total interest: draw interest $= 343.75 \times 120 = \$41{,}250$; repayment interest $= 427.39\times 240 - 50{,}000 \approx \$52{,}573.60$. Overall $ \approx \$93{,}823.60 $.

Frequently Asked Questions (FAQ)

Does this calculator account for changing rates or rate caps?

No. It models constant rates for each phase. To stress test, try higher/lower draw or repayment APRs.

What CLTV limit should I use?

Common caps are 75%–90% depending on occupancy, credit, and lender. Use your lender’s quoted maximum when available.

Is the draw payment always interest-only?

Many HELOCs are interest-only during the draw, but some allow or require principal payments. Check your agreement.

Are closing costs or annual fees included?

No. This tool excludes fees, taxes, and insurance. Incorporate them separately for a full budget.

Can I model multiple draws?

This version assumes a single lump-sum at the start. For multiple draws, approximate by summing interest for each draw or compare scenarios.

What happens if my requested draw exceeds the estimated maximum?

The tool will flag the scenario as infeasible. Reduce the draw, increase home value, lower mortgage balance, or adjust the CLTV limit if your lender allows.

Is this a credit offer?

No. Results are estimates for planning only and are not a loan approval or rate quote.

Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Board.
Last reviewed for accuracy on: September 13, 2025.