AnswersWhen a client won't pay
When is an invoice officially late?
The short answer
After the agreed date. With none agreed, the law gives 30 days from delivery or their getting your invoice, whichever is later1. The later day is day 1, and interest runs from day 312, so nobody gets to pay whenever they like. Even an agreed date has a limit: 60 days with a business, 30 with a public authority, and a longer business term holds unless it is grossly unfair to you2.
England and Wales only. WolfX is software, not a law firm.
The numbers
What sets the date, and what it costs.
What you can add
A £2,000 invoice with no agreed date
Say you emailed another business an invoice for £2,000 on 3 September 2026 and delivered the work on 10 September. You agreed no payment date. The 30 days begin with the later of the two days2, so 10 September is day 1 and 9 October, a Friday, is day 30. Interest starts on Saturday 10 October. Counted from the invoice date, it would have started a week early. On 30 November it is still unpaid: 52 days late. It went late in the second half of 2026, so the rate is the 3.75% base rate8 plus 8%7, which is 11.75%.
From here it grows by £0.64 a day until it is paid.
The road ahead
Five steps. All free.
Step 1: Look for a date you agreed
Check your quote, order, contract and emails. A date you both agreed counts2, in writing or not, and so does a rule that works one out, such as 14 days after the invoice.
If the client ignores it, it stays the date. A phrase like end of month counts only if you agreed it; it is not the law.
Step 2: No date? Count 30 days from the later day
Take the later of two days1: the day you delivered or the day they got your invoice. That day is day 1. Day 30 is the last day to pay without interest2, and day 31 is the first late day.
A checking or sign-off step in your deal can move the start to the day after the check2, within limits the law sets.
Step 3: Check the date isn't too long
With a business, a later date you agreed holds unless it is grossly unfair to you. If it is, interest starts after day 602 of that same count.
With a public authority the fairness test does not apply: interest starts after day 30 even if the contract says later. Most public contracts also carry a built-in term to pay valid, undisputed invoices within 30 days4.
Step 4: Name the first late day
The due date itself is not late. The next day is the first late day, and the first day you count for interest. Section 4 of the Late Payment of Commercial Debts (Interest) Act 19982 counts days and says nothing about weekends, so as written a due date on a Friday means interest starts on the Saturday.
From that day you can charge interest and work it out to the day.
Step 5: Put the date in writing next time
Send the email below before the next job starts. A yes gives you a date you can point to. If they want a different date, you find out before the work, not after it.
A letter you can copy
Email confirming the payment date
Send it when a job is agreed and before the work starts, so the date is in writing from the first day.
Tap a highlighted gap to see what goes in it.
Send it by email so it is dated, and keep a copy with the quote or order. If they reply with a different date, agree one by email before you start, and keep the reply that settles it.
When not to bother
When it isn't worth it
- Your customer is a private individual. The Act covers contracts where both sides are acting in the course of a business3; a sale to a private customer follows other rules.
- You already have an agreed date inside the limits. Interest starts the day after it, so skip step 2. The 30-day rule only fills a gap.
- They dispute the work, not the date. Then the question is what they owe, not when. Ask for the undisputed part first and settle the rest separately.
- It went late yesterday and the client is worth keeping. Interest has started, but on £2,000 it is £0.64 a day, so a call or an email first costs you nothing.
- Your agreed date runs past 60 days. Whether a longer term is grossly unfair is a judgement on all the facts2, so ask a solicitor who does commercial debt recovery before you rely on it.
The Wolf's note
With no date agreed, the clock starts when the last of two things has happened: the work landed, and the bill arrived. Write both days on the file before you chase. Then day 31 is a date they can check for themselves.
Mr. Wolf · the AI inside WolfX
What comes next
Your next move
What you can add
How do I work out late payment interest to the day?
Multiply the invoice by the yearly rate, divide by 365, then multiply by the days late.
6 min read · Letter included
Can a big company make me wait 60 or 90 days to be paid?
Up to 60 days. With a business, a longer date is not banned, but it holds only if it is not grossly unfair to you; otherwise interest starts on day 61.
5 min read · Letter included
So it doesn't happen again
What payment terms should I put on my invoice?
Fourteen or thirty days, agreed before the work starts.
5 min read · Letter included
Don't want to do this yourself?
The Wolf does every step for you. He works out the sums, writes the letters and keeps track of every date. Nothing goes without your yes.