Calculator Inputs
Complete the fields below. After submission, the result stays above this form and below the header.
Example Data Table
Use these sample cases to verify the flow and compare how balance timing changes the estimated interest-only payment.
| Case | Credit Limit | Opening Balance | Net Activity | APR | Average Daily Balance | Estimated Payment |
|---|---|---|---|---|---|---|
| Scenario 1 | $100,000.00 | $45,000.00 | $3,000.00 | 8.25% | $47,200.00 | $320.05 |
| Scenario 2 | $150,000.00 | $90,000.00 | $5,000.00 | 9.10% | $94,032.26 | $736.85 |
| Scenario 3 | $75,000.00 | $20,000.00 | $500.00 | 7.60% | $19,666.67 | $122.85 |
Formula Used
The calculator uses balance timing to estimate interest more accurately than a simple month-end check.
1) Effective APR
Effective APR = Direct APR when direct mode is selected.
Effective APR = Reference Rate + Margin when indexed mode is selected.
2) Average Daily Balance
Average Daily Balance = ((Opening Balance × Billing Days) + (New Draws × Average Draw Days) - (Payments × Average Payment Days)) ÷ Billing Days
3) Daily Rate
Daily Rate = Effective APR ÷ 100 ÷ Day-Count Basis
4) Estimated Interest-Only Payment
Interest-Only Payment = Average Daily Balance × Daily Rate × Billing Days
5) Utilization and Reserve
Utilization = Principal Before Interest ÷ Credit Limit × 100
Suggested Reserve = Estimated Payment × (1 + Reserve Buffer %)
How to Use This Calculator
Follow these steps for a faster and cleaner estimate.
Frequently Asked Questions
Plain HTML answers, kept concise for quick reading.
1) What does interest-only payment mean for a HELOC?
It is the interest charged for the billing cycle without paying down scheduled principal. Your lender may still require fees, past-due amounts, or other charges, so the actual minimum due can be different from this estimate.
2) Why does this calculator use average daily balance?
Many revolving credit accounts calculate interest from how balances change day by day. Average daily balance captures the timing of draws and payments better than using only the ending balance.
3) When should I use direct APR mode?
Use direct APR when your statement or lender portal already shows the exact annual rate for the billing cycle. This avoids rebuilding the rate from an index and margin.
4) When should I use prime plus margin mode?
Use indexed mode when your HELOC rate floats with a published benchmark and a contract margin. Enter both parts so the calculator can estimate the effective APR automatically.
5) What does the day-count basis change?
A 360-day basis produces a slightly higher daily rate than a 365-day basis at the same APR. Your statement agreement should indicate which method your lender uses.
6) Why is the stress-test payment useful?
Variable-rate HELOCs can reprice quickly. Stress testing helps you see whether your cash flow can absorb a rate increase before the next billing cycle arrives.
7) Can this estimate replace my lender statement?
No. It is a planning tool. Actual billed interest may differ because of posting dates, fees, introductory terms, rate caps, rounding, and lender-specific statement conventions.
8) Why export the results to CSV or PDF?
CSV is useful for spreadsheets, budgeting models, and comparisons across multiple rate scenarios. PDF is helpful when you want a clean record to share or save.