Interest note — guide

An interest note is a document used to calculate and communicate interest for late payment. It is not an invoice, but it helps to document the calculation clearly.

When an interest note is issued

Most often after a payment deadline has passed. It is common in B2B relations where documentation matters.

Interest note vs invoice vs payment reminder

• Invoice documents the sale or service.
• Payment reminder is a formal request to pay.
• Interest note specifies the interest amount and calculation period.

What the note should include

• parties’ data,
• basis of the claim (e.g., invoice number),
• delay period,
• interest rate,
• calculated interest amount,
• issue date and payment deadline.

How to calculate interest

amount × annual rate × number of days / 365

Use the interest calculator for a fast estimate.

Delivery and proof

Send the note in a way that provides proof of delivery (email confirmation or postal receipt).

Practical scenarios

• B2B delay: the note clarifies the calculation and the period.
• Rent payment: the note documents interest for late rent.

Common mistakes

• missing delay period,
• wrong rate,
• interest calculated on the wrong amount.