Late payment is usually a process problem

Most clients who pay late are not dishonest — they are busy, and your invoice had no clear due date, no payment details, and no consequence for waiting. Fix the process first, and most "late payers" disappear.

Prevention: the invoice itself

• Send the invoice the day the work is delivered — not at the end of the month.
• Put a real due date on it ("Due: 14 March"), not just "Net 14".
• Include your full bank details on the invoice so paying takes one minute.
• Add a late-fee line. Simply existing, it moves your invoice up the pile.
• Always send a PDF, never an editable file.

The follow-up schedule

• 3 days before the due date: a friendly heads-up. "Just flagging that invoice #001 is due Friday — copy attached in case it helps." Attach the invoice again; half of all "lost invoices" really were lost.
• On the due date: a short, warm reminder that payment is due today, with the amount and the payment details repeated.
• 3–7 days overdue: firmer and factual. State the number of days overdue, restate the late-fee term from the invoice, and ask for a payment date.
• 14+ days overdue: send a formal past-due notice. Keep it professional and in writing, pause any ongoing work, and state the next step clearly.

Wording that works

Short, factual, and free of apology. Never "sorry to bother you" — you are owed this money. State the invoice number, the amount, the due date, and exactly what you need: payment, or a date by which it will be made.