Understanding your HELOC results
The table below contrasts the two phases of a HELOC, since the shift from interest-only to fully amortizing payments is what produces the payment jump this calculator quantifies.
| Phase | Payment covers | Balance | Typical duration |
|---|---|---|---|
| Draw period | Interest only (in this model) | Stays at the drawn amount | Often 5–10 years |
| Repayment period | Interest + principal (fully amortizing) | Declines to zero | Often 10–20 years |
- Most HELOCs carry a variable interest rate tied to an index such as the prime rate, so the actual payment can change during both the draw and repayment periods; this calculator uses a single fixed rate for simplicity.
- Real HELOC balances typically fluctuate as a revolving line — borrowers draw and repay over time — whereas this calculator assumes the full amount is drawn once and held flat for the entire draw period.
- The calculator excludes any annual or draw fees some lenders charge, and it does not model a HELOC used with interest-only payments extending into the repayment period on some lender structures.
What is a HELOC?
A home equity line of credit is a revolving credit line secured by a borrower's home equity. The Consumer Financial Protection Bureau explains that a HELOC has a draw period, during which the borrower can withdraw funds and typically pays interest only on the amount drawn, followed by a repayment period, during which no further draws are allowed and the outstanding balance is repaid through fully amortizing principal-and-interest payments.
During the draw period, because payments cover interest only, the balance does not decline from making the minimum payment — it stays at whatever amount has been drawn, similar in structure to an interest-only mortgage. When the repayment period begins, the lender recalculates the payment needed to fully pay off that same balance over the repayment term, which produces a materially higher monthly payment than the draw-period minimum.
This calculator assumes the full drawn amount is outstanding for the entire draw period and that no further draws or paydowns occur before repayment begins — a simplified model of the interest-only-to-amortizing structure, since actual HELOC balances typically fluctuate as a revolving line.
How to use this HELOC calculator
- Enter the amount drawn on the line of credit (the balance you expect to carry).
- Enter the HELOC's annual interest rate — HELOCs are commonly variable-rate, so use the current rate.
- Enter the length of the draw period in years, during which payments are interest-only.
- Enter the length of the repayment period in years, during which the balance fully amortizes.
- Read the interest-only payment, the higher repayment-period payment, the size of the jump between them, and the total interest across both phases.
The formula behind HELOC payments
During the draw period, the interest-only payment is simply the drawn balance multiplied by the monthly interest rate, since no principal is being repaid. During the repayment period, the standard amortization formula is applied to the same balance (because it was never reduced during the draw period) over the stated repayment term.
Worked example: a $50,000 balance at 8.5% with a 10-year draw period and a 15-year repayment period has an interest-only payment of $354.17 per month during the draw period. Once repayment begins, the amortizing payment on the same $50,000 balance over 15 years is $492.37 — a payment increase of $138.20. Total interest across both phases (10 years of interest-only payments plus 15 years of amortizing payments) is $81,126.56.
Common mistakes
- Assuming the interest-only draw-period payment will continue for the life of the line — it applies only during the draw period, after which repayment requires a materially higher amortizing payment.
- Not budgeting for the payment jump when repayment begins, especially since HELOC rates are often variable and can rise independently of the phase change.
- Treating the drawn balance as fixed when in practice a HELOC is revolving — additional draws during the draw period increase the balance the repayment-period payment will be based on.
- Overlooking that a variable rate can change the interest-only payment during the draw period even if the drawn balance does not change.
- Confusing a HELOC's draw-period interest-only payment with a home equity loan's payment, which is typically fully amortizing from the start on a fixed lump sum.
Häufig gestellte Fragen
What is the difference between the draw period and the repayment period?
During the draw period, a HELOC borrower can withdraw funds and typically makes interest-only payments on the amount drawn, so the balance does not decline from the minimum payment. During the repayment period, no further draws are allowed and the outstanding balance is repaid through fully amortizing principal-and-interest payments, which are materially higher than the draw-period interest-only payment.
Why does my HELOC payment jump so much when repayment starts?
Because interest-only payments during the draw period do not reduce the principal, the full drawn balance is still outstanding when repayment begins, but now it must be repaid over a fixed, often shorter repayment term. Spreading that balance over the repayment period with a payment that now covers principal as well as interest produces a significantly higher monthly payment — for example, $354.17 to $492.37 on a $50,000 balance at 8.5% with a 10-year draw and 15-year repayment.
Are HELOC interest rates fixed or variable?
Most HELOCs carry a variable interest rate, commonly tied to an index such as the prime rate, meaning the payment can change during both the draw and repayment periods as the index moves. Some lenders offer a fixed-rate option on all or part of the balance; borrowers should confirm which structure applies to their specific line.
Does a HELOC work like a credit card?
In structure, yes — a HELOC is a revolving line of credit, meaning a borrower can draw, repay, and redraw funds up to the credit limit during the draw period, similar to a credit card. It differs in that it is secured by home equity, generally carries a lower rate than unsecured credit, and converts to a fixed amortization schedule once the draw period ends.
Can I pay principal during the draw period?
Most HELOCs allow voluntary principal payments during the draw period even though only interest is required, and doing so reduces both the outstanding balance and the size of the eventual repayment-period payment. This calculator models the minimum interest-only payment scenario; making additional payments during the draw period would produce a lower balance entering repayment than shown here.
Quellenangaben
- Consumer Financial Protection Bureau (CFPB). What you should know about home equity lines of credit. consumerfinance.gov.
- Consumer Financial Protection Bureau (CFPB). What is a home equity line of credit (HELOC)? consumerfinance.gov.
- Federal Reserve Board. Consumer Handbook on Adjustable-Rate Mortgages / home equity lending guidance. federalreserve.gov.
- Freddie Mac. Understanding mortgage options and loan types. freddiemac.com.
- Brueggeman WB, Fisher JD. Real Estate Finance and Investments. 15th ed. McGraw-Hill Education, 2019.