Corbelworks · Collections Math

Late Invoice Interest & Carrying Cost Calculator

See what an unpaid ticket is costing you: accrued interest at your contract rate, optional flat late fee, and the daily burn while the balance sits open.

Everything runs in your browser. No numbers are sent anywhere, nothing is stored, works offline once loaded.

Part of the contractor late invoice interest guide — past-due carrying cost and collection ask math.

Not legal advice. Enter the annual rate and late fee from your contract or terms. This tool does simple arithmetic only. It does not assert statutory entitlements, state-law rates, or that any amount is collectible.

1 · Invoice & rate

Invoice balance still owed, before interest or late fees.
$
From your signed terms / purchase order. Use 0 to see days late and flat fee only.
%/yr
The day payment was due under the invoice or contract.
Today, or the date you expect payment / are writing the ask.
One-time fee from your terms (e.g. $50 admin). Leave 0 if none.
$
365 is the common contractor default for simple annual interest; 360 is bank-style.
days
Method, formulas & limits

What this calculates

Simple interest on unpaid principal for calendar days past due, plus any flat late fee you enter from the contract. It is a carrying-cost and collection-ask worksheet, not a determination of legal rights.

Formulas

  • Days late = max(0, as-of date − due date) in whole calendar days.
  • Accrued interest = principal × (annual rate / 100) × (days late / day-count basis).
  • Daily carrying cost ≈ principal × (annual rate / 100) / day-count basis (when rate > 0).
  • Total to request (math) = principal + accrued interest + flat late fee.

What this deliberately does not do

  • Does not look up or assert state statutory rates, prompt-pay acts, or prejudgment interest statutes.
  • Does not compound interest, apply grace periods, or model partial payments.
  • Does not certify that interest or fees are enforceable under your contract or jurisdiction.

Sources & assumptions

  • Simple interest and day-count conventions are standard commercial arithmetic (principal × rate × time).
  • Defaults are illustrative placeholders. Confirm the rate, fee, and due date in the signed agreement before sending a collection ask.
  • Outputs are calculations only — not legal, tax, accounting, or collections advice.