HELOC Draw Period Cost Calculator — Rex's Toolbox

Rex says

Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.

Try a scenario

Click to load — tweak from there.

Inputs

HELOC balance drawn($)

Current variable rate during draw period(%)

Years left in draw period

Expected rate at start of repayment(%)

Repayment period length(years)

Result

Payment increase when repayment starts

$49

Current interest-only payment

$356

Full amortizing payment at repayment

$405

Total interest paid, remaining draw period

$25,650

Payment multiplies by

1.1

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How to use this

1Enter heloc balance drawn ($).
2Enter current variable rate during draw period (%).
3Enter years left in draw period.
4Enter expected rate at start of repayment (%).
5Enter repayment period length (years).
6Read your payment increase when repayment starts on the right — it updates as you type.
7Hit Share to keep the scenario or send it to someone.

About this calculator

Most HELOCs have a draw period (commonly 10 years) where you can borrow, repay, and re-borrow, often paying interest-only, followed by a repayment period (commonly 20 years) where the balance amortizes fully and payments jump substantially. This calculator estimates your interest-only payment during the draw period at a variable rate, projects what happens if you only make interest payments the entire draw period, and shows the payment shock when repayment begins — a scenario that catches a lot of HELOC borrowers off guard because the draw-period payment can be a third or less of the eventual repayment-period payment on the same balance.

FormulaInterest-only payment = balance × (rate ÷ 12). Repayment-period payment = balance amortized over the repayment term at the (possibly different) repayment-period rate. Payment shock = repayment payment − interest-only payment.

Worked example

Using the values the calculator loads with:

Inputs

HELOC balance drawn: 45000 $
Current variable rate during draw period: 9.5 %
Years left in draw period: 6
Expected rate at start of repayment: 9 %
Repayment period length: 20 years

Results

Payment increase when repayment starts: $49
Current interest-only payment: $356
Full amortizing payment at repayment: $405
Total interest paid, remaining draw period: $25,650
Payment multiplies by: 1.1

What each field means

Inputs

HELOC balance drawn ($): The heloc balance drawn used in the calculation, measured in $. Starts at 45000 $ so you have a working example on load.
Current variable rate during draw period (%): The current variable rate during draw period used in the calculation, measured in %. Starts at 9.5 % so you have a working example on load. Accepted range: 0–18 %.
Years left in draw period: The years left in draw period used in the calculation. Starts at 6 so you have a working example on load. Accepted range: 0–15.
Expected rate at start of repayment (%): The expected rate at start of repayment used in the calculation, measured in %. Starts at 9 % so you have a working example on load. Accepted range: 0–18 %.
Repayment period length (years): The repayment period length used in the calculation, measured in years. Starts at 20 years so you have a working example on load. Accepted range: 5–30 years.

Results

Payment increase when repayment starts: Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Current interest-only payment: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Full amortizing payment at repayment: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Total interest paid, remaining draw period: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Payment multiplies by: Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

Why does the repayment-period payment jump so much?

During the draw period you're typically paying interest only, so none of the balance shrinks. When repayment begins, the same balance must fully amortize — principal plus interest — over the repayment term, which is usually a much bigger monthly number than interest alone, especially if the balance hasn't dropped at all during the draw years.

Can I pay down principal voluntarily during the draw period?

Yes, and it's the single best way to avoid payment shock. Any principal you pay down during the draw period reduces both the balance subject to interest now and the balance that gets amortized into a bigger payment later — even modest extra payments meaningfully soften the transition.

Is a HELOC rate fixed or variable?

Almost all HELOCs carry a variable rate tied to the prime rate (prime plus a margin), so your interest-only payment can rise even without drawing more money if the Fed raises rates. Some lenders offer a fixed-rate conversion option on all or part of the balance — worth asking about if rate risk worries you.

What happens if I can't afford the repayment-period payment?

Options include refinancing the HELOC into a fixed home equity loan, doing a cash-out refinance to roll it into your first mortgage, or negotiating a modification with your lender. Address it well before the draw period ends — waiting until the payment jumps limits your options and negotiating leverage.

Accuracy and limitations

Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.

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Cite this calculator

Writing about this topic? Grab a citation — every link helps keep these tools free.

APA

RevenueLab. (2026). HELOC Draw Period Cost Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/heloc-draw-cost

HTML

<p>Source: <a href="https://www.revenuelab.fyi/toolbox/heloc-draw-cost" target="_blank" rel="noopener">HELOC Draw Period Cost Calculator — RevenueLab</a> (2026).</p>

Markdown

Source: [HELOC Draw Period Cost Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/heloc-draw-cost) (2026).