HELOC Calculator
Two questions answered in one tool: how much can you borrow against your home, and what will it actually cost — with optional rate-shock scenarios for the variable repayment-period rate.
Phase breakdown
| Phase | Term | Monthly payment | Phase interest |
|---|
| Scenario | Repayment payment | Repayment-phase interest | Lifetime cost |
|---|
What is heloc calculator?
A HELOC — home equity line of credit — is a revolving line of credit secured by your home, conceptually closer to a credit card than a mortgage. You’re approved for a maximum line, you draw against it as needed, and you pay interest only on what you’ve drawn. The line is bounded by your home equity: the lender adds your existing first mortgage to the proposed line, divides by the home’s appraised value, and caps the ratio (CLTV) at typically 80–90%. So a $500,000 home with a $300,000 mortgage and an 85% CLTV cap supports a maximum line of $125,000.
A HELOC’s life splits into two distinct phases. The draw period — usually 10 years — is when you can borrow against the line and your monthly payment is interest-only. On a fully drawn $100,000 line at 8.5%, that’s about $708/month. The repayment period — usually 20 years after draw ends — locks the balance and amortizes it to zero like a regular mortgage. The same $100,000 at 8.5% over 20 years comes to about $868/month. The jump from $708 to $868 is what’s commonly called payment shock, and on rates that have risen during the draw period the jump can be considerably larger. The calculator’s rate-shock toggle exists specifically to show you that scenario.
The variable rate is the structural risk that makes HELOCs different from fixed mortgages. Your rate is almost always prime plus a margin (e.g. prime + 0.5%), and prime moves with the federal funds rate. When the Fed hikes 100 bps, your HELOC rate hikes 100 bps the next month or quarter. The calculator’s default mode assumes today’s rate persists for the whole 30-year span — a useful baseline but not a forecast. Use the rate-shock toggle to see what +1/+2/+3 percentage points would do to the repayment-phase payment; the draw payment is held at today’s rate because today’s rate is known.
A few caveats. The calculator models the standard HELOC structure: full draw at month 1, interest-only during the draw period, fully amortizing P&I during the repayment period. It does not model annual fees (typical $50–100/year), draw fees, early-termination fees, partial draws or paydowns during the draw period, or interest-only HELOCs that never enter a repayment phase (these exist but are rare). It also does not handle the mortgage-interest tax deduction, which depends on the use of funds and your overall AGI under current US tax law — talk to a tax professional.
Privacy. Every calculation runs locally in your browser. Your form inputs are saved to your own browser’s localStorage so a refresh doesn’t lose them, but the data never leaves your device — there’s no server, no API, no analytics on input values. The storage key is heloc-calculator:inputs:v1. To wipe it, use your browser’s “clear site data” tool.
This is not financial advice. This calculator is a math tool. Whether to take out a HELOC, a home-equity loan, or a cash-out refinance depends on your specific equity, income, other debts, the planned use of funds, and your tolerance for variable-rate risk — consult a financial professional before tapping home equity.
When to use a heloc calculator
- Sizing your line before you apply — Most lenders cap combined LTV at 80–90% of your home's appraised value. Plug in your home value, your remaining first-mortgage balance, and the lender's CLTV — the tool returns the most you could realistically draw. Useful for setting expectations before you spend an afternoon on an application.
- Estimating draw vs. repayment payments — A HELOC's draw period is interest-only — your payment is small. When the repayment period kicks in, you're suddenly paying down principal too, and the payment can roughly 1.5–2× overnight. The Cost mode shows both numbers side by side so the jump isn't a surprise.
- Comparing a HELOC to a cash-out refi or home-equity loan — A HELOC is variable-rate revolving credit; a cash-out refi is a brand-new fixed-rate first mortgage; a home-equity loan is a fixed-rate second mortgage. This calculator handles the HELOC side; pair it with our mortgage-payoff calculator to see what a cash-out refi at today's rates would actually cost.
- Stress-testing against rate hikes — Toggle Show rate-shock scenarios to see what your repayment-phase payment looks like at +1, +2, and +3 percentage points above today's rate. The draw payment doesn't move — today's rate is known — but the repayment payment is at the mercy of the rate when the draw period ends.
- Modeling debt consolidation — If you're considering moving high-rate credit-card balances onto a HELOC, plug the consolidated total into the line amount and the HELOC's APR. Compare the lifetime interest to what you'd pay on the cards. Remember: cards are unsecured, but a HELOC puts your home on the line.
- Sanity-checking what a lender quotes you — If a HELOC officer quotes a number that feels off, run the same numbers here. Real differences usually come from origination fees, annual fees, or a different rate-index assumption — none of which this calculator models. The base math (interest-only draw + amortizing repayment) is exact.
How to use the HELOC Calculator
- Start in Borrow mode and find your max line — Enter your home value, current first-mortgage balance, and the CLTV cap your lender uses (most cap at 85%; aggressive lenders go to 90%). The Max HELOC line is the maximum you'd qualify to draw — though you don't have to draw the full amount.
- Hand off to Cost mode — Click Use this in cost calculator on the result. The line amount carries over and the calculator switches modes, so you can immediately see what borrowing that much would cost.
- Tune the cost inputs — Adjust line amount, draw years (typically 10), repayment years (typically 20), and current APR (today's HELOC rates run roughly 7.5–9.5%, but check your lender's actual quote). The four payment + cost figures update on every keystroke.
- Toggle rate-shock to see the worst case — Tick Show rate-shock scenarios to add a 4-row table showing your repayment payment at +1/+2/+3% above today's rate. This is the shock you'd feel if rates rise materially before the draw period ends.
Worked examples
Borrow capacity on a $500k home with a $300k mortgage
Input: Home value $500,000 · 1st-mortgage balance $300,000 · Max CLTV 85%
Output: Max HELOC line $125,000 · Available equity $200,000 · Current LTV 60.0%If your lender allowed 90% CLTV instead, you'd qualify for $150,000.
$100k draw at 8.5% with a 10/20 split
Input: Line $100,000 · Draw 10 years · Repayment 20 years · APR 8.5%
Output: Draw payment $708.33/mo · Repayment payment $867.82/mo · Lifetime interest $193,277.58 · Lifetime cost $293,277.58The repayment payment is ~22% higher than the draw payment — the classic HELOC payment shock.
Rate-shock on the same line
Input: Same as above, with Rate-shock toggle ON
Output: Repayment at +1% $932.13/mo · +2% $998.38/mo · +3% $1,066.43/moEven a +2% shock pushes the repayment payment 15% higher than today's; useful as a stress test.
Frequently asked questions
What's the difference between a HELOC, a home-equity loan, and a cash-out refinance?
What's CLTV and why do lenders cap it?
What is "payment shock" at the end of the draw period?
Is HELOC interest tax-deductible?
What happens if interest rates rise during the draw period?
Does this calculator save my data?
heloc-calculator:inputs:v1; clear your browser's site data to wipe it.