Calculator Form
Use preset IRS ranges for included 2026 quarters, or enter your own annual rate. Dates outside the included preset ranges use the fallback rate.
Example Data Table
| Scenario | Debt Amount | Period | Annual Rate | Method | Approx. Interest | Approx. Total |
|---|---|---|---|---|---|---|
| Standard debt, 30 days | $10,000.00 | 30 days | 6.00% | Daily | $49.44 | $10,049.44 |
| Standard debt, 90 days | $25,000.00 | 90 days | 6.00% | Daily | $372.33 | $25,372.33 |
| Large corporate, 120 days | $50,000.00 | 120 days | 8.00% | Daily | $1,332.49 | $51,332.49 |
Formula Used
Daily Compounding
Daily Rate = Annual Rate / 365
Ending Balance = Principal × (1 + Annual Rate / 365)Days
Interest = Ending Balance − Principal
Simple Interest
Interest = Principal × Annual Rate × Days / 365
Ending Balance = Principal + Interest
When you choose the IRS preset option, the calculator applies the matching preset rate day by day. If your date range includes uncovered dates, the fallback rate handles those extra days.
How to Use This Calculator
- Enter the tax debt amount.
- Choose your start and end dates.
- Select the taxpayer type.
- Pick IRS presets or a manual annual rate.
- Choose daily compounding or simple interest.
- Set a fallback rate for uncovered preset dates.
- Press Calculate Interest.
- Review the result summary, graph, and segment table.
- Export the report as CSV or PDF if needed.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates interest growth on a tax debt balance over a selected date range. It focuses on interest only. It does not automatically add penalties, fees, or other balance changes unless you reflect them in your entered amount or rate choice.
2. Why are there preset and manual rates?
Preset rates help you model included IRS quarter ranges faster. Manual rates help when you need another period, a planning assumption, or a custom review scenario. That makes the page useful for both quick checks and detailed debt planning.
3. Should I use daily compounding or simple interest?
Use daily compounding when you want a closer growth model for IRS-style interest. Use simple interest when you need a rough planning estimate, a comparison case, or a cleaner internal worksheet for early budgeting.
4. What happens if my dates cross two rate periods?
The calculator splits the timeline into segments and applies the matching rate to each day. That creates a more realistic result than one flat rate. You can review every segment in the results table after submission.
5. Does this include IRS penalties too?
No. This page is built for interest estimation. Penalties can materially change your total balance, so they should be modeled separately. You can add known penalties to the starting debt if you want one combined planning figure.
6. Can corporations use this calculator?
Yes. There is a standard underpayment option and a large corporate underpayment option. Choose the setting that matches your case, then confirm your dates and rate source before calculating the projected interest cost.
7. Why would I enter a fallback rate?
The fallback rate covers dates not included in the built-in preset windows. It prevents blank calculations and lets you keep working. This is especially useful when your debt period stretches beyond the prepared quarter list.
8. Do the CSV and PDF buttons save my data online?
No. They generate downloads in the browser from the current result shown on the page. Nothing is stored by the export feature itself. Server logging and hosting behavior still depend on your own environment.