What is a dunning letter and when should you send one?

A dunning letter is distinct from a routine payment reminder: it is more formal, it explicitly states the overdue status, and it usually indicates the consequences of non-payment — such as late fees, credit hold, or referral to a collections agency. The word 'dunning' signals to both the sender and the recipient that this is not a casual nudge but a formal step in a collection process.

Dunning letters typically come in graduated stages. A first-stage dunning letter, sent around 14 to 21 days past due, is firm but assumes good faith — the customer may have missed the invoice. A second-stage letter, around 30 to 45 days, states consequences explicitly. A third and final dunning letter, sometimes called a final demand letter, gives a specific deadline and explicitly states that referral to collections or legal action will follow if payment is not received.

The legal weight of a dunning letter depends on how it is written. A letter that threatens legal action must be accurate — if you do not actually intend to file in small claims court or hire a collections agency, the threat is toothless and may damage your credibility. For service businesses, keeping early-stage dunning letters factual and consequence-free is usually more effective than going straight to threats, which can poison a recoverable customer relationship.