HELOC Calculator: Draw & Repayment Payments

Scenario	Draw	Repayment	Δ vs base
-1% (8.000%)	$333	$418	$-32
Current (9.000%)	$375	$450	$0
+1% (10.000%)	$417	$483	+$33
+2% (Stress) (11.000%)	$458	$516	+$66

HELOC calculator: draw period, repayment, and CLTV

Models interest-only draw payments and amortizing repayment on a home equity line of credit (HELOC), with combined loan-to-value (CLTV) and a +2% rate stress test. Holds the variable rate flat for projection; results are illustrative, not a lender quote.

What this calculator does

The widget projects monthly payments for a home equity line of credit through two phases: interest-only during the draw period, then principal plus interest during repayment. Enter home value, first-mortgage balance, credit-line amount, prime rate + margin (prime may load from live data), optional first-year intro rate, and draw/repayment lengths. Outputs include draw and repayment payments, repayment jump, total interest, CLTV, a payment-over-time chart, and rate sensitivity at −1%, current, +1%, and +2%. It assumes the full withdrawn balance stays outstanding through draw, does not model partial draws, fixed-rate conversion segments, fees, or state-specific rules.

Draw (interest-only):

$P_{\text{draw}} = B \times \frac{r}{12}$
Repayment (amortizing):

$P_{\text{repay}} = B \times \frac{r/12\,(1+r/12)^{n}}{(1+r/12)^{n} - 1}$
CLTV:

$\text{CLTV} = \frac{\text{Mortgage} + \text{HELOC}}{\text{Home Value}} \times 100$

How the math works

With the default inputs, the home is valued at $500,000, the first mortgage balance is $300,000, the lender max CLTV cap is 80%, and the HELOC balance drawn is $50,000. Combined loan-to-value (CLTV) is the first mortgage plus the HELOC balance divided by home value. The maximum credit line at 80% CLTV is 80% of $500,000 minus $300,000, which equals $100,000. CLTV on this scenario is ($300,000 + $50,000) ÷ $500,000, or 70%. That exceeds the widget’s 65% safety guide and triggers the amber CLTV warning.

Most HELOCs price as prime rate plus a fixed margin. With the default 8.5% prime and 0.5% margin, the ongoing annual rate is 9%. During the first 12 draw months, the introductory rate of 5% applies instead. On a $50,000 balance, the year-one interest-only payment is about $208 per month (balance times 5% divided by 12). After month 12, the draw payment uses the ongoing 9% rate: $50,000 × 9% ÷ 12, or about $375 per month. When the 10-year draw period ends, repayment amortizes the same $50,000 over 240 months at 9%, which is about $450 per month. That is a $75 per month step above the ongoing draw payment.

Total interest equals draw-period interest plus repayment-period interest. Draw-period interest includes the intro year and the remaining interest-only months. Repayment interest is total repayment payments minus the principal balance. At these defaults, total interest is about $101,000. The +2% stress test reruns both phases at 11% ongoing. On the same $50,000 balance, the stress draw payment is about $458 per month and the stress repayment payment is about $516 per month.

Limits of the model

Real HELOCs may allow partial draws, rate caps, fixed-rate conversion segments, annual fees, and lender-specific freeze rules after appraisal drops. This calculator holds the withdrawn balance flat, applies intro rate only to the first 12 draw months, and does not model tax deductibility or debt-to-income approval. Use section 05 sensitivity and a fixed home equity loan comparison before treating variable payments as long-term affordable.

HELOC Calculator FAQ

What is the difference between the draw period and the repayment period?

In section 03 Timeline, the Draw period (years) field (default 10) sets interest-only payments on the withdrawn balance. When draw ends, the Repayment (years) field (default 20) switches the widget to principal plus interest. The dark results card labels ongoing draw vs Repayment (year 11) and shows the repayment jump in dollars per month.

How does prime rate plus margin affect my HELOC payment?

Section 02 Rates adds Prime (%) and Margin (%) into the read-only Ongoing variable field. At default 8.5% prime and 0.5% margin, the ongoing rate is 9%. That rate feeds draw-phase interest (after the first-year intro) and the repayment amortization in section 05 Rate sensitivity. Prime may refresh from live data after the page loads.

What is CLTV and why does 65% matter?

Combined loan-to-value (CLTV) is (first mortgage + HELOC balance) ÷ home value. The widget computes it from section 01 Equity & limits and shows CLTV on the dark results card. Above 65%, an amber warning appears under the inputs. Default scenario: $500,000 home, $300,000 mortgage, $50,000 drawn → CLTV 70%.

What is repayment shock and how do I prepare?

Repayment shock is the jump when interest-only draw ends. At defaults ($50,000 drawn, 9% ongoing), the widget shows draw ≈ $375/month, repayment ≈ $450/month, and a +$75/month step on the results card and in the Payment step panel. Prepay during draw, bank the difference, or compare a fixed home equity loan before year 11.

Is HELOC interest tax-deductible?

Only when funds pay for qualifying home improvements under current mortgage-interest rules. This calculator does not model tax treatment; it projects payments and interest cost only. Keep receipts and confirm with a tax professional. Results here are not tax advice.

What happens if prime rises 2%?

Section 05 Rate sensitivity includes a +2% (Stress) row. On $50,000 drawn at 9% ongoing, draw rises from about $375/month to $458/month and repayment from about $450/month to $516/month. The dark card also shows Stress P&I for quick reference.

How does the intro rate work in this calculator?

The Intro rate (%) field in section 02 (default 5%) applies only to the first 12 draw months. Year-one interest-only on $50,000 drawn ≈ $208/month. Months 13 through the end of draw use the ongoing variable rate (9% at defaults). Section 04 Payment over time shows the lower plateau before ongoing draw payments.

What does the strategy chip on the results card mean?

The dark HELOC model card shows a chip such as Balanced, Liquidity safe (CLTV ≤ 65%), Repayment risk (large payment jump), or Equity maxed (near the max CLTV cap). At defaults (70% CLTV, +$75 jump), the chip reads Balanced while the CLTV warning still appears because leverage exceeds the 65% safety guide.

HELOC Calculator

Equity & limits

Rates

Timeline

Payment over time

Rate sensitivity

How to use this calculator

Reading draw vs repayment payments

Example: $500K home, $300K mortgage, $50K drawn

Section 04 payment step chart

CLTV warning in section 01

Section 05 rate sensitivity table