Calculate interest on overdue payments using simple, monthly-compounded, or daily-compounded accrual with optional grace periods, flat late fees, and interest caps.
When payments are overdue, the actual charge often depends on more than one annual rate. Some agreements use simple daily interest, others compound monthly or daily, many include a grace period before interest starts, and some layer on a flat late fee or a contractual cap on how much interest can accrue.
This calculator models those moving parts in one worksheet. It calculates the overdue interest, adds any flat late fee, applies an optional cap, and shows a 30-day accrual schedule so the numbers are easier to audit. It is meant as a planning and comparison tool, not as a statement of what is legally recoverable in every jurisdiction.
Overdue-payment clauses are easy to misread when compounding, grace periods, fees, and caps are buried in contract language. This page makes those assumptions visible so you can compare the different charging structures before using the number in a budget, demand, or negotiation.
Simple Interest = Principal × (Annual Rate / 365) × Chargeable Days Monthly Compounding = Principal × ((1 + Annual Rate / 12)^(Chargeable Days / 30) − 1) Daily Compounding = Principal × ((1 + Annual Rate / 365)^(Chargeable Days) − 1) Chargeable Days = max(Days Overdue − Grace Period, 0) Total Penalty = min(Interest, Cap if any) + Flat Late Fee
Result: $197.26 in accrued interest under simple interest
Daily interest = $10,000 × (0.08 / 365) = $2.1918/day. Over 90 days: $2.1918 × 90 = $197.26. Total owed = $10,197.26.
Simple interest grows only from the original principal. Monthly or daily compounding adds prior interest back into the balance, which changes the path of the charge over time. This page lets you compare those methods directly instead of assuming every overdue-payment clause works the same way.
A short grace period can erase the first several days of accrual, while a flat late fee can matter more than the interest in short-delay scenarios. That is why the worksheet keeps the fee and the interest separate before combining them into the total penalty.
This page is useful for checking arithmetic and comparing clause structures. It does not determine which rate is legally permitted, whether compounding is enforceable, or whether a court will award the same amount.
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This worksheet applies straightforward interest math to overdue balances using the selected method: simple daily accrual, monthly compounding, or daily compounding. It also layers in the optional grace period, flat late fee, and interest cap so users can compare common clause structures in one place.
The page is intentionally conservative. It does not determine whether a charge is legally enforceable, whether a particular rate is allowed in a given jurisdiction, or whether a court would award the same amount. It is a reference worksheet for checking arithmetic and comparing contract language after the governing law is known.
Per diem means "per day." The per diem reference is the annual rate divided by 365, applied to each day the balance remains unpaid. This page shows that simple daily reference even when you are comparing it against a compounded method.
That depends on the governing law, the type of obligation, and whether the charge is contractual, prejudgment, post-judgment, consumer, or commercial. This page helps with the math once you know the applicable rate; it does not determine which jurisdictional rate applies.
The page can model simple interest, monthly compounding, or daily compounding. Simple interest is still common in many overdue-payment and judgment contexts, but some contracts expressly allow compounding.
Sometimes, but not automatically. Whether both charges can be collected depends on the contract, the governing law, and any reasonableness, usury, or consumer-protection limits that apply to the transaction.
If a judgment or contract uses simple daily accrual, multiply the principal by the applicable annual rate, divide by 365, and multiply by the number of chargeable days. This page does not determine which legal rate applies; it only helps with the arithmetic once you know it.
Yes, interest accrues every calendar day, including weekends and holidays. Unlike business-day calculations, interest runs continuously from the date the payment became overdue.