How to use this calculator
A HELOC payment can jump sharply when the draw period ends and repayment begins — and again if a variable rate rises. This tool shows the interest-only payment, the repayment-stage amortized payment, and both figures at a second rate you choose, so the jump is visible before it happens.
Enter your own figures in the form above. A blank field is treated as missing — not as zero — so the tool will ask you to complete it. A genuine zero is accepted where it makes sense (for example, no HOA dues). Press Calculate for a breakdown, Load worked example to fill in the example below, or Reset to return to the defaults.
Formula and assumptions
Interest-only monthly payment = balance × annual rate ÷ 1200; principal remains unchanged. Repayment payment = balance × r ÷ (1 − (1 + r)−n) over the repayment term. Both are shown at the entered rate and at the second scenario rate.
Worked example
Worked example: $50,000 balance at 9%, interest-only mode. Monthly interest $375; principal remains $50,000. At 11% the interest-only payment would be $458.33. Enter a repayment term to see the amortized repayment payment alongside these figures.
Use the Load worked example button above to reproduce this example in the form, then change one input at a time to see what drives the result.
Limitations and common mistakes
HELOCs are commonly variable-rate with draw/repayment structures, fees, minimum draws and lender-specific conversion options that this tool does not model. No draw is approved or promised here, and a variable rate is not predicted — the second rate is a scenario you choose, not a forecast.
Frequently asked questions
Why does the payment jump at repayment?
Because interest-only payments do not reduce principal. Repayment-stage payments must cover both interest and principal over the remaining term.
Is interest-only “cheaper”?
Per month, yes; over time, no — the principal is still owed in full at the end of the draw period.
What if my rate changes monthly?
Re-run the tool at the new rate. This is a scenario calculator, not a rate tracker or forecast.
Sources
Estimates only. Results from this calculator are not a loan offer, appraisal, engineering design, equipment selection or contractor quote.