About the HELOC Calculator
A home equity line of credit gives you flexible access to your home's equity, and payments work differently depending on whether you're in the interest-only draw period or the fully-amortizing repayment period. Our HELOC Payment Calculator shows both.
How It Works
The calculator computes the interest-only payment (just the monthly interest charge on your balance, common during a HELOC's initial draw period) and separately computes the fully-amortizing payment (principal plus interest, spread evenly across your repayment term) for direct comparison.
Formula & Methodology
A HELOC's two phases use fundamentally different payment math. During the draw period, the interest-only payment is just balance × monthly rate - none of it reduces principal, so the balance stays flat unless you voluntarily pay more. Once the repayment period begins, the outstanding balance is amortized like a standard loan over the remaining term, which is why the payment typically jumps meaningfully higher at that transition - it now has to cover both ongoing interest and principal reduction within a fixed number of remaining months.
Step-by-Step: Calculating It By Hand
- 1For the interest-only payment: multiply the outstanding balance by the monthly interest rate.
- 2For the amortizing payment: apply the standard loan payment formula to the balance, rate, and remaining repayment term in months.
- 3Compare the two to see the payment increase that will occur when the draw period ends.
Examples
Interest-only draw period
A $40,000 HELOC balance at 9% has an interest-only payment of $300/month - low, but none of it reduces the principal balance.
Repayment period
The same balance switching to a 15-year fully-amortizing repayment period at the same rate produces a significantly higher monthly payment, since it now includes principal.
Advantages
- Shows both interest-only and amortizing payments so the transition isn't a surprise
- Useful for budgeting for a HELOC that's about to exit its draw period
- Works for any balance, rate, and repayment term
- Makes the low initial payment versus higher long-term payment trade-off concrete
Common Mistakes
- Budgeting only around the low interest-only payment without planning for the higher amortizing payment later
- Forgetting HELOC rates are usually variable, meaning payments can rise if rates increase
- Using a HELOC for ongoing expenses rather than a specific purpose with a clear repayment plan
- Not accounting for the risk that a HELOC is secured by your home, unlike unsecured credit
Edge Cases to Watch For
- HELOC rates are typically variable, tied to an index like the prime rate, so both the interest-only and amortizing payments can change over time even without any new borrowing.
- Continuing to draw funds during the draw period increases the balance the eventual amortizing payment will be calculated on.
- Some HELOCs offer a fixed-rate conversion option for all or part of the balance, which would use a different, locked payment calculation than this variable-rate comparison.
- Missing the transition from interest-only to amortizing payments in a household budget is one of the most common HELOC payment shocks borrowers experience.
Common Use Cases
- Understanding the payment jump when a HELOC exits its interest-only draw period
- Budgeting for a HELOC repayment period in advance
- Comparing a HELOC's payment structure against a home equity loan
- Planning how to pay down a HELOC balance before rates rise further