A home equity line of credit (HELOC) calculator can help estimate how much you might draw against home equity and how the payment could change when repayment begins. This calculator uses the home value, first-mortgage balance, maximum loan-to-value (LTV) limit, amount drawn, APR, and period lengths you enter.
The result is a mathematical estimate, not a lender's approved credit limit or a forecast of your future rate. HELOC agreements differ, so compare the calculator's assumptions with the line's terms before using it to plan payments. The CFPB notes that HELOC payments can rise when repayment begins and that the home may be at risk if you cannot repay; review its HELOC overview alongside your contract.
How to Use the HELOC Calculator
- Enter the home figures: Type the Home Value, the Mortgage Balance still owed on the first mortgage, and the Max LTV, typically 80% to 85%; these set the estimated credit line.
- Describe the draw: Enter the Amount Drawn, what you will actually borrow, and the HELOC APR, which is usually variable.
- Pick the draw payment: Under Draw-Period Payment, choose Interest only for the draw-period option or Amortizing (pay principal early).
- Set both periods: Enter the Draw Period in years and months (1 to 10 years) and the Repayment Period in years and months (5 to 30 years).
- Optionally test a rise: Enter a Rate-Rise Scenario (points), such as 2, to see both payments again at the higher APR.
- Calculate and read the results: Click Calculate to see the credit line and amount still available, the payments while drawing and while repaying, and the total interest and total repaid.
The model holds the APR constant, but a real HELOC rate is prime plus a margin, so treat the payment figures as estimates that can move.
Estimate a line from home value and mortgage balance
The calculator estimates the combined loan limit by multiplying the home value by the LTV percentage you enter. It subtracts the existing mortgage balance to estimate the credit line, then checks that the planned draw does not exceed that amount:
Estimated credit line = (home value ? selected LTV limit) - existing mortgage balance
For example, a $300,000 home at an 85% LTV limit gives a modeled combined balance limit of $255,000. Subtracting a $220,000 first-mortgage balance leaves an estimated $35,000 line ? most of the property's equity is already committed to the first mortgage, and the line is only the remainder. If $20,000 is drawn, the model shows $15,000 remaining. Lenders may use different property values, LTV limits, liens, and qualification criteria; this arithmetic does not determine approval.
HELOC or home equity loan ? which to model?
Model the HELOC when the spending arrives in stages or the final amount is uncertain: an unused line costs nothing in interest, the draw payment tracks the drawn balance, and the rate moves with the market in both directions. Model the home equity loan when the amount is fixed and known: one lump sum, a fixed rate, and level payments for the whole term, with no adjustment risk. The trade is flexibility against a locked rate and payment ? and the same house secures either, so the combined balance is what each tool's LTV limit tests.
Draw-period payment options
Enter the APR and draw-period length. The calculator offers two draw payment methods:
- Interest only: It estimates the monthly payment as the drawn balance multiplied by APR and divided by 12. The principal remains unchanged during the modeled draw period.
- Amortizing: It calculates a level payment over the draw period and reduces the balance as principal is paid. The remaining balance then becomes the starting amount for the repayment estimate.
Interest is calculated using the entered APR in monthly periods. The tool does not model daily accrual, changing monthly balances from additional withdrawals, or lender-specific minimum-payment rules.
What changes when repayment begins
At the end of the draw period, the calculator amortizes any remaining balance over the repayment period you entered, using the same APR. Its result compares the modeled draw payment with this repayment payment, so you can see the change under those assumptions.
For instance, using a $50,000 draw for illustration (larger than the $35,000 line above) at 8% APR, with an interest-only draw period of 120 months and a 240-month repayment period, the estimated draw payment is $333.33 per month. The remaining $50,000 is then modeled at $418.23 per month during repayment. The difference is $84.90 per month. The draw and repayment periods are inputs, not fixed defaults or a prediction of your lender's schedule.
Choosing the repayment term
The repayment length is the lever that decides how hard the recast hits. Keeping the $50,000 balance and 8% APR fixed, the calculator returns these payments for the three repayment lengths it allows:
| Repayment term | Monthly repayment | Rise from the $333.33 draw payment | Interest during repayment |
|---|---|---|---|
| 60 months | $1,013.82 | +$680.49 | $10,829.18 |
| 120 months | $606.64 | +$273.31 | $22,796.36 |
| 240 months | $418.23 | +$84.90 | $50,369.52 |
The trade is stark: the 60-month repayment clears the balance for roughly a fifth of the interest the 240-month schedule charges, but it demands three times the monthly payment. A HELOC quoted with a long repayment period is not cheaper; it is the same debt spread thinner. If the repayment term in the agreement is short, the payment shock is the number to plan for, not the draw payment.
A worked renovation case
Take the $50,000 renovation drawn under an interest-only draw period of 24 months and a 240-month repayment period at 8% APR. During the draw, the payment is $333.33 ? pure interest ? and the balance is still exactly $50,000 at month 24, after $8,000.00 of draw-period interest. Repayment then amortizes the untouched $50,000 over 240 months at $418.23, adding $50,369.52 of interest. The total modeled cost of the renovation is $108,369.52 repaid, of which $58,369.52 is interest: on these terms, the financing costs more than the work itself. Choosing the amortizing draw option raises the draw payment but shrinks the repayment payment and the total, because the balance falls during the draw instead of standing still.
Test a higher APR
The optional rate-rise field adds the entered percentage points to the APR and recalculates the draw and repayment payments at the higher rate. In the example above, a two-point increase changes the assumed APR from 8% to 10%; the calculator estimates $416.67 during draw and $482.52 during repayment.
This is a what-if comparison, not a forecast. It applies the higher APR to both modeled phases rather than predicting when a lender will adjust the rate. The calculator does not model an index, margin, rate cap, or periodic reset schedule. Use the variable-rate terms in your agreement for a contract-specific estimate.
What the rate caps do in your agreement
Neither cap is an input here, which is why the rate-rise field applies one permanent shock rather than a path of adjustments. The caps live in your agreement: a periodic cap bounds how much the rate can move at a single adjustment, and a lifetime cap bounds how far it can rise over the life of the line. The practical step is to read both numbers in your own agreement, then re-run this calculator with the rate field set at your lifetime ceiling ? your worst case is your contract's ceiling, not the generic two-point bump. A line with a high lifetime cap can move much further than that example; a line with a low cap limits the damage but may also adjust downward more slowly when the index falls.
Model limitations
- The draw period runs 12 to 120 months and the repayment period 60 to 360 months; the calculator cannot model a facility with longer phases or different payment rules.
- The line-sizing arithmetic uses only the value, first-mortgage balance, and LTV limit you enter. It does not assess income, credit, other liens, or lender underwriting, and it is not an approved line amount.
- The model excludes annual fees, draw charges, and closing costs, and interest is calculated monthly on the drawn balance only. Unused-line fees and suspension or freeze terms are not modeled.
- The rate-rise scenario applies one permanent shock to both phases at once. It does not model an index, a margin, adjustment timing, or rate caps, so it is neither a forecast nor a quote for a future payment.
- Tax treatment of the interest is not evaluated here; ask a qualified tax professional about your circumstances.
To compare a revolving line with a fixed lump-sum second mortgage, use the Home Equity Loan Calculator. For a first-mortgage payment estimate, see the Mortgage Calculator. For an unsecured borrowing estimate, try the Personal Loan Calculator.
The line of credit itself is not a payoff tool: the calculator prices the draw and repayment costs you enter rather than modeling the entire first mortgage. To pay off a mortgage balance with extra monthly money, use the Mortgage Payoff Calculator.
Provenance: every dollar figure in this article was computed by replicating the calculator's model (apps/tools/heloc-calculator/logic.php and the shared whole-cent annuity engine) from the stated inputs, and verified in October 2026.
Last verified: October 2026. Calculator figures are outputs for the inputs entered; they are not live quotes, current rates, or an offer.