James Whitfield
You've delivered the work, the client is delighted, and the invoice lands in their inbox. Then nothing happens for weeks. When you finally chase, the reply is: "Sorry, we couldn't process it — there's no PO number on here." Most late payments aren't the result of awkward clients or tight-fisted finance teams. They're caused by small, entirely avoidable errors on the invoice itself. Fix those, and you'll spend far less time chasing and far more time billing.
Why Small Errors Cost More Than They Seem
A single query on an invoice rarely costs you a day. It usually costs you a fortnight. Many businesses only run payment twice a month, so anything flagged for correction misses the current run and rolls into the next one. For a freelancer waiting on a £2,000 invoice, that's a very real gap in the household budget; for a small limited company, it's payroll you have to cover from reserves.
There's a reputational cost too. Invoices are one of the few bits of admin your client sees consistently. Consistent mistakes — wrong totals, missing references, vague terms — quietly suggest you're disorganised, which makes conversations about raising your rates considerably harder later on.
Missing or Inconsistent Reference Numbers
Every invoice needs a unique, sequential number, and it needs to stay put. Reusing numbers, restarting the sequence mid-year, or inventing formats on the fly creates confusion in your client's accounting system and in yours when it comes to your own records.
- Pick one format and stick to it — for example, INV-2025-014. It's readable, sortable, and dates itself.
- Always include a client PO number if they've given you one. Many accounts payable systems will reject an invoice without it, regardless of how good your work was.
- Never reissue an amended invoice under the same number. If something needs correcting, issue a credit note and a fresh invoice.
- Quote the invoice number everywhere — in the email subject line, on the PDF filename, and in the payment reference.
Your invoice should also carry the basics without prompting: your business name and address, the client's legal entity name, the invoice date, a clear description of the work, and your payment details.
Totals, VAT and Rounding That Don't Add Up
Arithmetic errors are the easiest mistake to make and the easiest to prevent. Check every line: hours multiplied by rate, expenses added once, discounts applied once. Then check the total actually matches the sum of the lines.
If you're VAT registered, show the rate clearly, display your VAT number, and state plainly whether your figures are inclusive or exclusive of VAT. If you're not registered, say so on the invoice — it heads off awkward questions and delays.
Rounding causes more rejections than you'd think. If your total comes to £1,250.005 and your client's system expects £1,250.00, the invoice can bounce entirely pending clarification. Keep everything to the penny, and let your accounting software do the calculations wherever possible. Spreadsheets are where these slips hide.
Vague Due Dates and Unclear Payment Terms
"Payment on receipt" sounds firm but means nothing. "30 days" is ambiguous if nobody knows when the clock starts.
- State the terms and the date. "Payment terms: 14 days from invoice date. Due date: 14 March 2025."
- Match what the contract says. If your engagement letter says 30 days, don't invoice on 7.
- Spell out your bank details in full — account name, sort code, account number — and tell them what reference to use.
- Mention late payment terms if you charge interest. A gentle line in your standard terms is often enough to keep things moving without confrontation.
Sending Invoices to the Wrong Place at the Wrong Time
Before you start a project, ask three questions: who processes invoices, which email address do they go to, and do you need a purchase order first? Getting answers on day one saves a fortnight of silence later.
Send your invoice as a PDF with a clear filename, such as INV-2025-014 - Consultancy - March.pdf. Avoid Word documents, screenshots, or totals typed into the body of an email.
Timing matters too. If your terms are 14 days, don't sit on the invoice until month-end. Send it the day you finish the work, or the day the milestone is signed off. Those few days often make the difference between landing in this month's payment run and the next one.
No Tracking Means No Leverage When Chasing
You can't chase what you haven't tracked. Keep a simple log — a spreadsheet will do — recording the invoice number, client, amount, date sent, due date and current status. Set a calendar reminder a couple of days before each due date, and again at seven and fourteen days overdue.
- At the due date: a short, friendly note. "Just checking this landed with you — happy to resend if not."
- A week overdue: confirm the invoice has been received and ask when payment is scheduled.
- Two weeks overdue: be firmer, restate the terms, and ask for a specific date.
- Beyond that: escalate in writing and reference your right to statutory interest on late commercial payments.
The trick is consistency. Most people stop chasing after one email because it feels awkward. The businesses that get paid on time are the ones that chase politely, reliably, and every single time.
