If you agreed a payment date
Where you and the customer agreed a payment date, that date is normally the starting point for deciding whether the invoice is late. Once the agreed date has passed without payment, the debt may be overdue.
GOV.UK says agreed payment periods must usually be within 30 days for public authorities or 60 days for business transactions. Businesses can agree a longer period than 60 days, but it must be fair to both businesses.
If you did not agree a payment date
If no payment date was agreed, GOV.UK says the payment becomes late 30 days after the later of two events: the customer receiving the invoice, or you delivering the goods or providing the service.
That means the date printed on an invoice is not always enough by itself. You may need to know when the customer actually received the invoice and when the work, goods or services were supplied.
Example: an agreed 30-day payment term
Suppose you issue an invoice and your contract gives the customer 30 days to pay. If the agreed due date passes and the invoice remains unpaid, the payment is late from the point determined by those agreed terms.
Keep the invoice, contract or written payment terms together so the due date can be checked before you calculate any late-payment amount.
Example: no payment date was agreed
Suppose the customer receives your invoice before the service is completed. Under the statutory fallback described by GOV.UK, the 30-day period runs from the later event, so the delivery or completion date can matter more than the invoice-receipt date.
If the dates are unclear or disputed, do not assume the calculator can resolve that factual question for you.
Does a late invoice automatically mean you can add interest?
No. A payment being late is only one part of the question. The statutory late-payment regime is aimed at qualifying commercial debts, and contractual interest provisions, disputes and the nature of the transaction can affect what applies.
If the debt may qualify, read our guide to charging late-payment interest and our guide to fixed recovery compensation before deciding what to include in a follow-up.
What to keep as evidence of the due date
Keep the original invoice, the contract or agreed payment terms, evidence of when the invoice was sent or received, and evidence showing when the goods or services were delivered. Those records can help explain why you treated a particular date as the payment due date.
If the invoice is already overdue, our unpaid-invoice guide sets out a practical sequence for reminders, evidence and proportionate escalation.
Official UK guidance
Check an overdue invoice
If you have an agreed payment due date and the invoice is overdue, use the free LatePay Kit calculator to check the basic eligibility questions and estimate potential late-payment interest and fixed recovery compensation.
Check my overdue invoice