HELOC Payment Calculator
A HELOC is two loans taped together: an interest-only draw period and an amortised repayment period, usually with a variable rate. Enter your current balance, the APR and the remaining years in each phase, and this calculator shows the monthly payment today and the payment jump you will see when repayment starts — the moment most HELOC borrowers feel for the first time.
How to project your HELOC payment
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1
Enter the current drawn balance
Use the most recent statement — the payment depends on what you owe, not on the full line.
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2
Enter the APR
Type your current variable rate; a sensitivity slider lets you stress test at +1%, +2% or +3%.
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3
Set draw and repayment lengths
Typical values: 10-year draw + 20-year repayment, but some products run 5+15 or 10+15.
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4
Compare both phases
See the interest-only draw payment now and the amortised payment that kicks in at conversion.
The two-phase payment structure
A HELOC’s payment math is simple once you split the phases.
Interest-only payment (draw phase)
Monthly payment = Balance × APR / 12
A $40,000 balance at 8.25% APR = 40,000 × 0.0825 / 12 = $275.00.
None of that payment reduces principal. If you only make the minimum, you will still owe $40,000 when the draw period ends.
Amortised payment (repayment phase)
Standard amortisation formula:
P = B × r / (1 − (1 + r)^−n)
where B is the balance at conversion, r is the monthly rate (APR / 12) and n is the number of monthly payments in the repayment period.
That same $40,000 at 8.25% over a 20-year repayment period:
P = 40,000 × 0.006875 / (1 − 1.006875^−240) ≈ $340.62/month
The jump from $275 to $340 looks small in this example, but increase the rate environment or the balance and the step can be brutal.
Sample payment steps
| Balance | APR | Draw (interest-only) | Repayment (20 years) | Jump |
|---|---|---|---|---|
| $25,000 | 7.5% | $156 | $201 | +$45 |
| $50,000 | 7.5% | $313 | $403 | +$90 |
| $100,000 | 8.5% | $708 | $868 | +$160 |
| $150,000 | 9.5% | $1,188 | $1,398 | +$210 |
Planning around the jump
- Pay principal voluntarily during the draw phase — even $200 a month compounds.
- Refinance to a fixed-rate second mortgage before repayment if rates have risen.
- Keep 3-6 months of the projected repayment payment in savings as a buffer.
Frequently Asked Questions
Most HELOCs charge a variable rate tied to prime. Even if your balance stayed flat, a prime rate hike changes your payment the same billing cycle. The calculator lets you stress-test at prime + 2% or + 3%.
Almost always yes. HELOCs typically allow unlimited prepayment, though some charge a small “early closure” fee if you close the line within the first 3 years.
Yes. Each additional draw during the draw period increases your balance, and your next interest-only payment rises accordingly. Some HELOCs bill weekly average balance, others month-end balance — read the disclosure.
The line freezes to new draws and the balance at that moment is amortised over the repayment term. Your first amortised payment is usually 20-40% higher than the last interest-only one at the same rate.
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