Free tool
Estimate an overdue invoice late fee from the invoice amount, due date, grace period, and fee terms. Use it as a worksheet, not legal advice.
Monthly, annual, or flat fee · Copyable summary · No invoice data uploaded
Inputs
Result
Use this as a billing worksheet. Laws and contract terms vary, so confirm any late fee before adding it to an invoice.
Days overdue
0
Late fee
$0.00
Estimated total
$2,370.00
Suggested wording
According to the payment terms on invoice, the balance is 0 days overdue. The estimated late fee is $0.00, bringing the estimated total due to $2,370.00.
Use the late fee calculator as a worksheet when an agreement already includes late-payment terms. Enter the unpaid balance, due date, payment date or calculation date, grace period, and the fee method named in those terms.
Suppose invoice #1042 has an unpaid balance of $2,370, was due 45 days ago, and the agreed terms use a 1.5% monthly fee with no grace period. The calculator prorates a monthly rate over 30-day periods:
The estimated total becomes $2,423.33. With a 10-day grace period, 35 days are chargeable: 35 ÷ 30 × 1.5% × $2,370 = $41.48. The difference is $11.85. Whether to apply or waive a fee depends on the agreement, the applicable rules, and the client relationship.
Monthly percentage. The calculator multiplies the balance by the stated monthly rate and prorates it using 30-day periods. This makes the estimate grow with the length of the delay.
Annual percentage. The calculator converts the stated annual rate to a daily amount by dividing the overdue period by 365. This is useful when the agreement or applicable rule quotes a yearly rate.
Flat fee. The calculator adds the fixed amount once after the grace period. It does not increase as more days pass unless the agreed terms expressly say otherwise.
Use the method and rate already stated in the agreement. Do not switch methods or invent a new charge after the invoice is late. Keep the original balance, fee method, chargeable days, fee, and estimated total separate so the client can review the calculation.
A calculator can check arithmetic, but it cannot decide whether a charge is allowed. Confirm the contract, transaction type, client location, and current local rules before adding a fee to an invoice, statement, or reminder.
It depends on the agreement and jurisdiction. Rules may differ between business-to-business and consumer transactions, and some systems provide statutory interest or recovery costs while others limit fees or require specific disclosures. A charge that appears only after payment is late may be treated differently from a term agreed before the work began.
Put payment and late-charge terms in the agreement before work starts, repeat the applicable wording on the invoice, and check the official rule for the transaction. For a material amount or a consumer invoice, get advice from a qualified professional in the relevant jurisdiction.
Show the original invoice amount, days overdue, grace period, fee method, estimated fee, and estimated total separately. Then use a calm overdue account reminder that asks for a payment date and gives the client a way to flag a missing approval or disputed detail.
You can estimate monthly, annual, or flat late fees based on the invoice amount, due date, and grace period you enter.
Late fee rules vary by contract, state, and country. This calculator is for planning only and is not legal advice.
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