Calculator Inputs
Example Data Table
| Scenario | Overdue Balance | Base Rate | Penalty Margin | Method | Penalty Days | Late Fee |
|---|---|---|---|---|---|---|
| Auto loan arrears | 8,000.00 | 7.25% | 3.00% | Simple | 20 | 35.00 |
| Credit line delay | 15,500.00 | 10.50% | 5.50% | Compound | 40 | 60.00 |
| Business invoice default | 22,750.00 | 9.00% | 6.00% | Simple | 55 | 100.00 |
| Mortgage installment delay | 3,200.00 | 6.80% | 2.20% | Compound | 15 | 25.00 |
Formula Used
1. Effective annual penalty rate
Effective Annual Penalty Rate = Base Annual Interest Rate + Penalty Margin
2. Charged penalty days
Penalty Days = max(0, Days Overdue − Grace Days)
3. Daily rate for simple penalty interest
Daily Rate = Effective Annual Penalty Rate ÷ Day-Count Basis
4. Daily equivalent rate for compound penalty interest
Daily Rate = (1 + Annual Rate ÷ Compounding Periods Per Year)Compounding Periods Per Year ÷ Day Basis − 1
5. Daily simple penalty accrual
Daily Interest = Current Principal × Daily Rate
6. Daily compound penalty accrual
Daily Interest = (Current Principal + Previously Accrued Interest) × Daily Rate
7. Total due
Total Due = Remaining Principal + Accrued Penalty Interest + Fixed Late Fee
When you enter a partial payment, the tool reduces principal on the chosen day. When you set an interest cap, further accrual stops once the cap is reached.
How to Use This Calculator
- Enter the overdue balance currently subject to penalty charges.
- Input the base annual interest rate from the loan or credit agreement.
- Add the contractual penalty margin charged after default or delay.
- Set the total overdue days and any allowed grace days.
- Choose simple or compound penalty interest, then select the day-count basis.
- For compound mode, select the compounding frequency used in your terms.
- Add any fixed late fee, optional partial payment, and optional cap.
- Submit the form to see summary metrics, graph trends, and schedule output.
- Use the CSV or PDF buttons to download your results.
Frequently Asked Questions
1. What is penalty interest?
Penalty interest is an extra charge applied when a borrower pays late. It is usually added to the normal interest rate or applied as a separate overdue rate under the contract.
2. Does this calculator work for invoices too?
Yes. It can estimate late charges for loans, revolving credit, installment debt, and overdue invoices whenever the agreement defines a base rate, penalty margin, and charge period.
3. What is the difference between simple and compound penalty interest?
Simple penalty interest charges interest only on overdue principal. Compound penalty interest adds new charges on principal plus previously accrued penalty interest, which usually produces a higher total.
4. Why does the day-count basis matter?
The day-count basis converts annual rates into daily rates. A 360-day basis produces a slightly higher daily charge than a 365-day basis for the same annual percentage.
5. How does the grace period affect results?
Grace days delay the start of penalty charging. If the overdue period is shorter than or equal to the grace period, no penalty interest accrues, though a fixed late fee may still apply.
6. Can I model a partial payment?
Yes. Enter a payment amount and the day it is made. The tool reduces principal on that day, which lowers future simple or compound penalty accrual.
7. What does the penalty cap do?
The cap limits accrued penalty interest to a percentage of the original overdue balance. Once that limit is reached, the calculator stops adding more penalty interest.
8. Are these results legally binding?
No. This is an estimation tool. Actual charges depend on your contract, lender notices, consumer law, court limits, and local regulations governing default interest and late fees.