Can I charge interest to a council, the NHS or another public body?
The short answer
Yes. The law counts a council or other public authority1 as a business, so the same interest at 8% over base rate5 and £40, £70 or £100 sum6 apply. A public body cannot delay interest past 30 days2, even if the contract says 60 or 90. Interest is not paid automatically10, so ask.
England and Wales only. WolfX is software, not a law firm.
What you can add
A £5,400 invoice to a council, on a 60-day contract
Say you finished a cleaning contract in June and a council received your £5,400 invoice on 6 July 2026. The contract says 60 days, but the law caps it at 30. The 30 days run from 6 July to 4 August, so interest starts on 5 August. On 30 September it is still unpaid: 57 days past the 30.
Then it grows by £1.74 a day until they pay. The contract's 60 days changed nothing. Interest started after 30.
The road ahead
Six steps. All free.
Step 2: Find your 30-day date
The 30 days begin on the later of the day you finished the work and the day they had notice of the amount2, usually the day your invoice reached them. A check-and-accept step in the contract can start them later, usually by no more than 30 days. Interest starts the day after the 30 days end. An earlier payment date in your contract still wins.
The aim to pay 90% of valid, undisputed invoices from small and medium-sized firms within 5 days is a policy target10. The 30 days is what interest hangs on.
Step 3: Check your invoice is valid
If your contract is a public contract8 under the Procurement Act 2023, the authority must pay within 30 days of receiving your invoice unless it considers the invoice invalid or disputes it9. If it does, it must tell you without undue delay.
A valid invoice names who is invoicing, describes what you supplied, gives the sum and has a unique number9, and meets any other requirement in your contract.
Step 4: Work out the sum
Interest that starts between 1 July and 31 December 2026 runs at 11.75% a year4: 8% plus the Bank Rate on 30 June3. Each day adds the invoice × 11.75% ÷ 365.
Add the fixed sum6 once. Here is how to work interest out to the day.
Step 6: If 14 days pass, go above the accounts team
Use the authority's own complaints route, then the Public Procurement Review Service11. It takes late payment cases from the last 2 years: publicprocurementreview@cabinetoffice.gov.uk10. Its recommendations are not binding. A devolved Welsh body's case goes to the Wales Procurement Review Unit.
The Small Business Commissioner is the wrong door. A public authority is not a 'larger business' in its Act12, so it can point you to the bodies that can help but cannot take your complaint.
Still unpaid? A letter before action comes before a court claim.
A letter you can copy
Email asking a public body for interest and the fixed sum
Send it once the 30 days have run out and a friendly reminder hasn't worked. Address it to the payments team and the contract manager, and copy the budget holder.
Tap a highlighted gap to see what goes in it.
Send it by email so it is dated. Copy the contract manager and the budget holder if you know who they are. Keep the sent email, the new invoice and the original invoice together in one folder.
When not to bother
When it isn't worth it
- The invoice is invalid or disputed. GOV.UK ties interest to an undisputed and valid invoice10, and the public-contract term falls away if the authority disputes it9. Sort it out first.
- It's a few days late and you want to renew. On a £5,400 invoice a day's interest is £1.74. A call to the contract manager may do more than an email with a sum in it.
- The buyer is a charity or a club. The Act does not name either, so check they're covered before you add interest.
- The contract is in Scotland or Northern Ireland. These pages cover England and Wales only, and the routes there differ.
The Wolf's note
A contract can say 90 days; for a public body, interest still starts after 30. Put the date and the sum in one email and ask whether they treat the invoice as valid. Either the money moves or they say why not in writing, and both are answers.
Mr. Wolf · the AI inside WolfX
What comes next
Your next move
Can I charge interest on a late invoice?
Yes, if you sold to another business.
3 min read · Letter included
When it first goes quiet
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
When it first goes quiet
What is the Small Business Commissioner, and can it help me get paid?
Yes, if you have fewer than 50 staff and your customer is a larger private business.
6 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.