What this tool calculates
This calculator estimates a late charge when an agreement expresses the charge as a daily percentage of the original overdue amount. It reports the charge for one day and the accumulated charge for the entered number of days. The result is an arithmetic estimate, not a decision that a fee is permitted or collectible.
The model is deliberately narrow. It uses the original amount as the base every day, so the calculation is simple rather than compound. It does not add yesterday's charge to today's base, calculate interest on fees, choose a grace period, or decide whether weekends count. Those details must come from the applicable contract and law.
Inputs
- Original amount is the overdue principal or installment on which the stated percentage applies. Enter it in one currency and read every monetary output in that same currency.
- Daily penalty rate is a percentage, not a decimal. Enter
2for 2%, not0.02. - Overdue days is a non-negative whole number. Day zero produces no accumulated fee. A partial day must first be handled according to the agreement's counting rule; the tool does not round it for you.
Before calculating, verify whether the rate is actually daily and whether it applies to the original balance, the missed installment, or another base. A monthly flat fee cannot be converted merely by typing its percentage into this field.
Method and formula
The calculator first converts the percentage to a decimal and finds one day's simple charge:
daily fee = original amount × daily rate ÷ 100
It then multiplies that unchanged daily fee by the count of overdue days:
total fee = daily fee × overdue days
No compounding occurs. If an amount is 500 and the daily rate is 2%, the calculation base remains 500 on every counted day. The interface displays two decimal places, but the contractual rounding point may be different. For reconciliation, keep the unrounded intermediate value until the final step unless the agreement explicitly requires daily rounding.
Worked example
Assume an invoice shows an original overdue amount of 500, a stated daily simple rate of 2%, and 10 counted overdue days.
- Daily fee: 500 × 2% = 10 per day.
- Total for 10 days: 10 × 10 = 100.
- The calculator therefore reports a daily fee of 10.00 and a total fee of 100.00 in the same currency as the original amount.
If the overdue-day input is zero, the daily reference amount remains 10.00 but the accumulated total is 0.00. That distinction helps check the rate without implying that a charge has already accrued.
How to interpret the result
Treat the output as a reproducible worksheet line. It can help compare an invoice with a written daily-rate clause, prepare an internal aging schedule, or identify which input needs clarification. Record the original amount, rate, due date, date-count convention, and calculation date alongside the result so another person can reconstruct it.
A different result does not by itself prove an invoice is wrong. Differences can arise from grace periods, caps, flat minimums, business-day rules, taxes, payments made during the period, or a rate applied only to the missed installment. Resolve those facts before relying on the number.
Accuracy and limitations
Late-fee rules vary by product, contract, and jurisdiction. Local law may cap a charge, prohibit it, require disclosure, or define the permitted base and timing. Some agreements use a fixed amount, a one-time percentage, continued contract interest, or a tiered schedule; none of those models is represented here. The calculator also ignores payments, credits, waivers, tax, collection costs, and currency conversion.
Use the signed agreement and current rules for the relevant place and transaction. For a disputed, regulated, or material charge, obtain appropriately qualified advice. This page is not personalized legal or financial advice and does not determine enforceability.
Sources
- Consumer Financial Protection Bureau, Regulation Z §1026.18 distinguishes disclosed late-payment charges from other amounts in covered credit transactions and illustrates why the governing terms matter.
- Consumer Financial Protection Bureau, Regulation Z §1026.34 contains transaction-specific restrictions for certain high-cost mortgages, demonstrating that a generic arithmetic result cannot substitute for the applicable rule.
Editorial record
Author: SoupCalc Editorial Team
Last reviewed: August 14, 2026
Review scope: Formula behavior, whole-day validation, contract boundaries, authority links, and the 500-at-2%-for-10-days example were checked against the implemented simple-rate function.