What Is a HELOC Payment Calculator?

A home equity line of credit, or HELOC, lets you borrow against the equity in your home as a revolving line rather than a single lump sum. You are approved for a limit, you draw what you need as you need it, and you pay interest only on the outstanding balance. Structurally the line has two chapters: an interest-only draw period while you spend, and an amortising repayment period during which the balance must be cleared. This calculator models both phases so you can see the payment you will face now and the much larger one waiting at the end of the draw period.

HELOC rates are variable, quoted as a margin over an index such as the US prime rate, so the rate you pay rises and falls with the market. The calculator takes the rate you are being charged and holds it flat so the numbers are readable, but the repayment payment should be treated as a rate-sensitive estimate rather than a fixed commitment.

How It Works

During the draw period the balance stays level because the payment covers only interest, so the monthly figure is simply the drawn amount multiplied by the monthly rate, which is the annual rate divided by twelve. Total draw-period interest is that payment multiplied by the number of months in the draw period. When repayment begins, the same balance is amortised into a fixed payment using PMT = P x r / (1 - (1 + r)^-n), where n is the number of months in the repayment term. Repayment interest is the sum of all those payments minus the principal, and total cost is the drawn balance plus both interest totals.

The calculator also divides your drawn balance by the home value to report the combined loan-to-value ratio, the figure lenders use to decide how large a line they will allow. If the CLTV exceeds the typical 80% guideline the result panel flags it, because exceeding that threshold usually means a smaller draw, a larger home value, or a specialist second-lien lender.

Understanding Your Results

The primary card shows the interest-only payment you make during the draw period and, directly beneath it, the amortising payment that takes over when the draw period ends. The gap between those two numbers is the payment shock that catches many borrowers out, and the reason financial planners advise paying principal during the draw period even when only interest is required. The breakdown table separates the two phases so the interest accumulated in each is visible.

Summary Statistics adds the available credit remaining on the line, the interest accumulated in each phase, the total cost of the borrowing, and the CLTV of your drawn balance. A practical strategy is to size the line well below your limit, pay extra principal during the draw years, and confirm with the lender whether a fixed-rate conversion or rate-lock option is available before repayment starts, since a variable rate that has drifted upward can make the repayment payment substantially higher than the figure modelled here.