Late payment interest claimer
A small system for any business that invoices other businesses: the due date established from the terms rather than assumed, the statutory rate pinned to the reference date it was fixed on, interest accrued daily, and the fixed compensation that is usually worth more than the interest. Seven posts on the same system, one diagram at a time, with a cost breakdown and an engineering reference at the end.
- 01
A late payment interest claimer on AWS for a few dollars a month
The whole system on one page — due dates, the rate, interest, the fixed sum and what you do with the number — and why the largest part of the entitlement sits on invoices that have already been paid.
- 02
When an invoice actually becomes late
Establishing a defensible due date for each invoice from the contract, the invoice terms or the statutory default, and recording which one applied.
- 03
The rate, and the date it was fixed on
How the statutory rate is determined and frozen: the two reference dates a year, the pinning rule, simple daily accrual, and when a contractual remedy displaces the statutory one.
- 04
Interest, compensation and costs: three claims, not one
The three components of a late payment entitlement, how they scale differently with invoice size, and how part payments and credit notes change the arithmetic.
- 05
Claiming it, waiving it, or just knowing it
Deciding what to do with a calculated entitlement: the branch that ends in a demand, the branch that ends in a visible concession, and the one that ends in a pricing conversation.
- 06
What the late payment interest claimer costs
About $4 a month. One Bedrock read per agreement is the only line that grows; the queue, the table, the mail and the storage are rounding errors. Plus the three ways the bill could surprise you.
- 07
Engineering reference: the late payment interest claimer architecture
Same system, drawn purely for engineers. Service names, region, Lambda inventory, IAM scopes, the schemas and the exact model id.
Frequently asked questions
- Can I really charge interest without agreeing it first?
- For business-to-business debts, yes. Where the contract is silent, a statutory right applies and it does not need the customer’s agreement. Where the contract does provide a remedy, that one applies instead, as long as it is a substantial one.
- What is the rate?
- Base rate plus eight per cent. The part people get wrong is which base rate: it is the one in force on the reference date at the start of the six-month period in which the debt became late, and it is then fixed for the whole life of that debt.
- What is the fixed sum?
- A flat amount per late invoice, on a three-band scale by invoice size, on top of the interest. On small invoices it is usually worth several times the interest, which is why it is the line most often left on the table.
- Can I claim on invoices that have already been paid?
- Yes. The entitlement arose when the invoice became late and it does not disappear when the principal is settled. It is an ordinary contract debt with the usual six-year window.
- What does it cost to run?
- A few dollars a month. See part six.