Accountants Late Payment Interest (Daily) Calculator FAQ
Answers to common questions about calculating daily interest on overdue invoices, including rates, days late and result accuracy.
This FAQ explains the calculator inputs, the daily simple-interest method and practical factors that can affect an overdue invoice interest estimate.
Using the calculator
Questions about the information needed to run an estimate.
What do I need to calculate late payment interest?
Enter the unpaid invoice balance, the annual interest rate and the number of days the payment is late.
What invoice amount should I enter?
Enter the currently unpaid balance before late payment interest. Reduce the amount for any credits or payments already applied.
What rate should I use?
Use the annual rate that applies under the relevant contract, policy or applicable rules. Confirm that rate independently before charging interest.
How should I count days late?
Use the number of calendar days from the applicable due date to the payment date or chosen calculation date, subject to the terms that apply.
Calculation method
Questions about the formula and results.
How is the daily interest charge calculated?
The calculator multiplies the overdue balance by the annual rate divided by 100 and divided by 365.
How is total late payment interest calculated?
The daily interest charge is multiplied by the number of days late.
Is the interest compounded?
No. The calculator uses simple interest on the original entered invoice balance.
What does total amount due include?
It includes the overdue invoice amount plus estimated interest. It does not include other charges.
Accuracy and assumptions
Questions about why an estimate may differ from a final amount.
Does the calculator use 365 or 366 days?
It uses 365 days for a consistent daily-rate conversion.
Can the rate change during the overdue period?
It can under some arrangements. If the applicable rate changed, calculate each period separately using the rate for that period.
Does the result include fees or compensation?
No. The result is interest only and excludes fixed charges, collection costs, taxes and similar items.
Why might my records show a different interest amount?
Differences can arise from day-count rules, start-date conventions, partial payments, rate changes and rounding methods.
Practical invoice scenarios
Questions about common overdue balance situations.
Can I calculate interest up to today?
Yes. Enter the unpaid balance and the number of overdue days up to your calculation date.
How do I handle a partial payment?
Calculate interest separately for the period before the payment and the period after it, using the applicable balance in each period.
Can I add the calculated interest to a payment reminder?
The calculator can provide an estimate, but whether and how interest may be claimed depends on the applicable terms and rules.
Can this calculator determine whether interest is legally chargeable?
No. It calculates an estimate from the inputs provided and does not determine legal entitlement.
How is daily late payment interest calculated?
Daily interest equals the overdue balance multiplied by the annual rate divided by 100 and then divided by 365.
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