Use this HELOC calculator to estimate your monthly payment during the interest-only draw period and your higher payment during the repayment period, plus total interest and the payment jump. It separates your credit limit from the balance you actually borrowed so your estimate is more realistic.
Advanced options
How to use this calculator
- Enter your Current balance drawn (the amount you actually borrowed, not the credit limit).
- Enter the APR during draw period and the Draw period length in years.
- Enter the Repayment period length in years.
- Choose Payment timing (most people use end of month).
- Open Advanced options if you want to: switch to Prime rate + margin, set a different repayment APR, add an extra monthly principal payment, or set a minimum draw payment.
- (Optional) To estimate a rough credit limit and CLTV, fill in Home value, First mortgage balance, and Max CLTV.
- Click Calculate.
- Read the two payments (draw vs repayment), the payment increase, and the total interest to see what changes your cost the most (usually rate, balance drawn, and repayment term).
Definitions
HELOC: Home Equity Line of Credit. A loan that lets you borrow against home equity, up to a credit limit.
Credit limit: The maximum you are allowed to borrow. Your payment is based on your balance drawn, not the limit.
Balance drawn: The amount you have actually borrowed right now.
Draw period: The first phase when you can borrow and often make interest-only payments.
Repayment period: The later phase when borrowing usually stops and you pay back principal plus interest.
APR: Annual Percentage Rate. The yearly interest rate as a percent used here to estimate your monthly rate.
Prime rate (index) and margin: A common way variable HELOC rates are set: APR equals Prime plus a fixed extra amount (margin). Prime is published as a reference interest rate [1].
CLTV: Combined loan-to-value. Your total loans on the home (first mortgage plus HELOC balance) divided by home value, as a percent.
Methodology
What this calculator models
This tool estimates a 2-phase HELOC: (1) an interest-only draw period and (2) a repayment period with a fixed monthly payment that pays the balance down to $0 by the end of the term. Many real HELOCs calculate interest daily and can change rates more often, so this is a planning estimate.
Step 1: Choose the APR used in each phase
Draw APR: If you choose Enter APR directly, the draw APR is the number you typed. If you choose Prime + margin, the draw APR is (prime rate + margin). Prime is a commonly published index rate [1].
Repayment APR: If you set Assume rate changes when repayment starts to Yes, the repayment APR is your entered repayment APR. If you leave repayment APR blank, the calculator uses the draw APR instead. If the toggle is No, the calculator uses the draw APR for repayment.
Step 2: Convert APR to a monthly rate
Monthly rate equals (APR percent / 100) / 12.
Step 3: Draw period payment (interest-only)
Interest-only monthly payment equals (balance drawn x monthly rate during draw). If you enter a minimum draw payment greater than that interest-only amount, the shown draw payment becomes the minimum. Note: depending on the lender rules, paying more than interest could reduce principal, but this calculator keeps the draw-balance constant for the draw-interest total estimate.
Step 4: Repayment period payment (principal + interest)
The repayment payment is the standard amortizing loan payment that pays off the starting repayment balance over n months, where n equals repayment years x 12. Payment equals balance start repay x (i / (1 - (1+i)^(-n))), where i is the monthly rate. If i equals 0, payment equals balance divided by n (to avoid divide-by-zero). This is the same core idea used in loan amortization math [2].
Step 5: Repayment interest and payoff months (with extra payments)
To include an extra monthly principal payment, the calculator simulates month by month: interest equals balance x i; principal paid equals (scheduled payment + extra payment) minus interest; new balance equals balance minus principal paid. It stops when the balance reaches 0 (final payment is capped so the balance does not go negative). If principal paid is not positive, the payment is not feasible at that rate because the balance would not shrink; the calculator returns N/A for payoff months and blocks the results with an error.
Step 6: Total interest outputs
Total interest during draw: balance drawn x monthly rate draw x (draw years x 12). This assumes the balance stays the same during draw.
Total interest during repayment: sum of monthly interest from the repayment simulation.
Total interest lifetime: draw interest plus repayment interest.
Optional: credit limit and CLTV estimates
If you enter home value and first mortgage balance, the estimated HELOC credit limit equals max(0, home value x (max CLTV / 100) minus first mortgage balance). Estimated CLTV equals ((first mortgage balance + balance drawn) / home value) x 100. If home value is missing or not positive, these are shown as N/A.
Rounding, formatting, and edge cases
Dollar outputs are rounded to cents and shown with comma separators. The calculator blocks impossible inputs (like blank required APRs, negative balances, or zero-year terms) and blocks non-feasible repayment scenarios where the payment would not cover monthly interest.