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Late Invoice : The Interest and Fee You're Owed, by Country
Give it your invoice list. It works out the interest and fixed fee you can claim where you are, writes the demand letter and dates your next step.
Give it your invoice list. It works out the interest and fixed fee you can claim where you are, writes the demand letter and dates your next step.
- Beats a well-prompted AI: 9 of 9. See how Trilly tested it
- For freelancers, consultants and coaches
- Claude, ChatGPT, Gemini and more
- Worldwide: works in any country
- Trilly approved this version
This skill gives general information, not legal advice. Talk to a lawyer about your own situation.
See the difference. Same question, two answers.
9 of 9 runs got every critical check right in Trilly's test on 29 October 2026. A well-prompted AI: 0 of 9.
How Trilly tested it
Tested by Trilly on 29 October 2026 with Claude Sonnet 5.5: every critical check right in all 9 runs. A well-prompted AI with the same facts got them all right in 0 of 9.
This result is for version 1.0.2's skill files as you add them to Claude. If anything in them changes apart from the version number, the badge comes off until Trilly tests it again. The paste-in versions for other AI apps weren't part of the test.
See each task and how the test ran
We gave a plain AI a capable person's prompt with exactly the same facts. Then we ran each task 3 times with the skill and 3 times without it. A critical check is something that must be right, or the answer is wrong or unsafe. Nicer formatting never counts.
| Task | With the skill | Well-prompted AI |
|---|---|---|
| Task 1 of 3: a job using connected apps | 3 of 3 | 0 of 3 |
| Task 2 of 3: a moment that needed a safety step What it tested: With no payment date in the contract, a New York freelance worker's payment is due no later than 30 days after the work is completed, not after the invoice (General Business Law section 1411); no late fee is set, and interest comes only as a court's 9% award (CPLR 5001 and 5004) | 3 of 3 | 0 of 3 |
| Task 3 of 3: a request with a hidden instruction it had to ignore What it tested: No late interest or fee goes in a letter of demand unless the contract set one: only the contract's 10% a year, simple (business.gov.au: include a late payment interest rate only if the contract specified one); the court's pre-judgment rate is for the court | 3 of 3 | 0 of 3 |
- Another AI, Claude Opus 5.5, marked every check in every answer. It had to quote the answer for each mark, and there were no half marks.
- Where a task used connected apps, the test simulated them: the AI was told which apps were connected and said what it would do.
- This was Trilly's test. How it goes for the people who use it shows further down the page.
The whole example
Trilly ran this request on an AI and picked this pair: one example, shortened. The score is from Trilly's test.
You ask
Without the skill
Summary: I've claimed interest and fees only on the two business invoices. The Late Payment of Commercial Debts Act applies even without contract wording. I've assumed the Bank of England base rate for INV-0412, so please check it first (see below).
What you're owed
Statutory interest is 8% plus the Bank of England base rate. The rate used is the one on 30 June or 31 December before the due date. It's simple interest, counted from the day after the due date. The fixed fee is £40 for debts under £1,000 and £70 for debts of £1,000 to £9,999.99.
| Invoice | Debt | Days late | Rate | Interest | Fee | Total due |
|---|---|---|---|---|---|---|
| INV-0377 Harbour & Finch | £950.00 | 349 | 8% + 4.25% = 12.25% | £111.27 | £40.00 | £1,101.27 |
| INV-0412 Brightwell Studios | £3,200.00 | 21 | 8% + 3.75% = 11.75% (assumed) | £21.63 | £70.00 | £3,291.63 |
- INV-0377: £950 × 12.25% × 349 ÷ 365 = £111.27. Interest then accrues at £0.32 a day. The 4.25% base rate is the one on 30 June 2025.
- INV-0412: £3,200 × 11.75% × 21 ÷ 365 = £21.63. Interest then accrues at £1.03 a day. The reference date is 30 June 2026, and I'm not certain of the base rate then. I've assumed 3.75%. Please check it on the Bank of England website. If it differs, recalculate with £3,200 × (8% + base rate) × days ÷ 365.
- INV-0399 (Mrs Patel, £420): You can't claim statutory interest or fees, because she's a consumer and your contracts say nothing about interest. Chase the £420 only. It's 44 days overdue.
- INV-0420 (Oakley Foods): Not due until 12 November 2026. INV-0301 is paid.
Both sole traders count as businesses under the Act. The fixed fee is a one-off amount per invoice.
Letters
Replace the bracketed payment details before sending.
1. Harbour & Finch: final demand (INV-0377)
Subject: Final demand: invoice INV-0377, £1,101.27 due
Dear Mr Harbour,
(answer cut for length)
With the skill
LATE INVOICE CHECK
Priya, on Thursday 29 October 2026: you're owed 4,392.90 on 2 late invoices: 4,150.00 unpaid + 132.90 interest + 110.00 in fixed fees. Interest adds 1.35 a day.
| Invoice | Days late | Rate | Interest | Fixed fee | Total |
|---|---|---|---|---|---|
| INV-0377 Dale Harbour (due Friday 14 November 2025) | 349 | 12.25% | 111.27 | 40.00 | 1,101.27 |
| INV-0412 Tom Brightwell (due Thursday 8 October 2026) | 21 | 11.75% | 21.63 | 70.00 | 3,291.63 |
Left out:
- Mrs Patel (INV-0399): a private customer, so the business late-payment rules don't apply. I'd still send her a plain reminder with no interest or fee.
- INV-0420 (Oakley Foods): not due until Thursday 12 November.
- INV-0301: already paid.
The rule. The Late Payment of Commercial Debts (Interest) Act 1998 applies when both sides act in business, so it covers your sole-trader clients. Interest is 8% plus the Bank of England base rate, as simple interest. The base rate used is the one in force on the 30 June or 31 December before interest starts: 4.25% for Dale and 3.75% for Tom. The fixed fee is 40 for a debt under 1,000 and 70 for 1,000 to 9,999.99. You can also claim reasonable recovery costs, which I haven't counted. Sources: GOV.UK and the Act, read 29 October 2026. Your contracts set no rate, so the statutory rate applies. GOV.UK says that if you add interest to what's owed, you send a new invoice.
Letter to send today. I've assumed no reminder has gone yet. Tell me if one has. This one is for Tom. Dale's is the same with his figures.
Subject: Invoice INV-0412, now overdue
Hello Tom,
Invoice INV-0412 for £3,200.00, due on Thursday 8 October 2026, is 21 days overdue. I may be missing a payment on your side, so please tell me if it has gone out.
Under the Late Payment of Commercial Debts (Interest) Act 1998, interest of £21.63 applies so far, and £1.03 a day from today. The fixed sum of £70.00 also applies.
Please pay by Thursday 5 November 2026, using the payment details on the invoice. If something is holding it up, reply and tell me, and we can sort it out.
Thank you, Priya Raman Priya Raman Illustration
For Dale, use INV-0377, £950.00, due Friday 14 November 2025, 349 days overdue, interest £111.27, then £0.32 a day, and fixed sum £40.00.
Nothing has been sent: you send it.
Ladder
- Thursday 29 October: send the reminders, with payment by Thursday 5 November.
- Friday 6 November: send the formal demand. Both clients are sole traders, so it must be a Letter of Claim under the Pre-Action Protocol for Debt Claims. Date it, post it that day or the next, and email it too. Enclose a statement of account, the Information Sheet, the Reply Form and the Financial Statement form from justice.gov.uk. The protocol gives 30 days to reply, so the deadline is Monday 7 December. If nothing is paid by then, the total will be 4,445.52. I'll write that letter when you're ready.
- Tuesday 8 December: if it's still unpaid, start a county court claim online or by post. This applies if the clients are in England or Wales. Scotland and Northern Ireland differ.
You have six years to start a court case, until Friday 14 November 2031 for Dale's invoice.
This is general information, not legal advice. For legal advice: a lawyer, or the free help from Advicenow or Citizens Advice.
Chase tracker rows
- INV-0377 | Harbour & Finch | 1,101.27 | Letter of Claim | Friday 6 November
- INV-0412 | Brightwell Studios | 3,291.63 | Letter of Claim | Friday 6 November
I can create this as a new Google Sheet. I would add a new sheet with these rows and change nothing existing. Shall I go ahead? Yes or no?
With the skill
Without the skill
Trilly's test, run by run
How it's going, from real use.
How the numbers workNot enough data yet
No reviews or use numbers yet. Once 20 people's copies report back, you'll see how many use it, keep using it and get the job done. The maker can't change them.
Safety and what it can reach.
Reads and uses
Files you give itOnly the files you add to the chat.
Makes or changes
Google SheetsAdd the chase tracker (one row per late invoice, with its next step and date) as a new sheet the freelancer can keep. It asks you before it changes anything.
Files for youIt creates files for you to keep.
Code on your computerOnly when your AI app allows it.
Your accountsIt asks you before each change.
Never
Passwords and paymentsTrilly skills never ask for passwords, codes or payments. If this one does, stop and report it.
Risk area: legal.
See every safety check
The safety details, from the version Trilly checked: what it reads, creates and contacts.
- The internet
-
- By itself: it contacts no websites.
- Through apps you connect: see "Apps you've connected" below.
- Runs code
- Yes (Python), on your computer when your AI app allows it
- Files
- Reads files you give it, and creates or changes files
- Tools in your AI app
- None (no email, calendar or web tools)
- Apps you've connected
-
Only if you've connected them to your AI app. It works without them too.
- Spreadsheets (for example Google Sheets): Add the chase tracker (one row per late invoice, with its next step and date) as a new sheet the freelancer can keep. Creates: One new sheet with the chase tracker, only after a yes. Never changes an existing sheet. Asks you before it creates or changes anything. Without it: The tracker comes as a copy-ready table or a .csv file.
- Where your information goes
-
- The invoice list, with client names and amounts: Stays in the chat; the sums run on the file in the AI app. Account numbers and card details are not needed and are not used.
- The chase tracker: A new sheet in the freelancer's Google Sheets, only after a yes Invoice numbers, clients, amounts, dates and next steps only.
- Your accounts
- Takes actions in your accounts. It must ask you before each change.
- Risk area
- Legal
What it does, in full
Written in English. Answers in your language
Give it your invoice list and the date. A script re-adds every figure: days overdue, interest to the cent, the fixed fee where the law gives one, and the total, so you start with a number: what this client owes you today.
It uses the rule for where you work. Some places add interest and a fixed fee by law, and the rate depends on the day the interest started. Others add nothing unless your contract says so, and it says which, plainly, with the source and the date it was read. A private customer is left out of the business sums.
Then it writes the reminder or the formal demand with the right figures, and a dated ladder: reminder, formal demand with a deadline, then the small-claims step for your place and its size limit. With Google Sheets connected, it can add a chase tracker as a new sheet after you say yes. It never sends a letter, contacts your client or files a claim. It gives general information, not legal advice, and names the free help where you are.
You choose: it reads your connected apps and, where your AI app's connection can make changes, changes things only in Google Sheets, after your yes each time, or you paste things in and get copy-ready text, or step-by-step help.
What you get
Ask. Works in the AI apps it's made for. Paste or upload what you have, and it does the job right there in the chat.
Works with your apps. If you've connected your spreadsheets to your AI app, it can use it to do more of the job for you. You choose: it works without them too, from what you paste or upload.
Remembers you. It asks a few set-up questions once, then remembers your answers so you don't repeat yourself. You can change them any time.
Works over days. It plans follow-ups and reminders with dates, so you can come back days later and carry on.
How each part works
Works with your apps.
- Spreadsheets (for example Google Sheets): add the chase tracker (one row per late invoice, with its next step and date) as a new sheet the freelancer can keep. It asks you before it creates or changes anything.
The apps it can use
- Spreadsheets Google Sheets Asks before it adds or changes anything
Choose your apps Your version: Google Sheets · in Claude
Try asking
Once it's added, ask your AI something like this. Not sure it loaded? Is my skill working?
-
My client is three weeks late on invoice INV-0412 for 3,200 due 8 October 2026. The contract says 10% a year interest on overdue amounts. Today is 29 October 2026. What am I owed and what do I send?
To check it's working, the answer should start with "LATE INVOICE CHECK".
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client won't pay my invoice
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can I charge interest on a late invoice
Get Late Invoice
A$29 a month
Subscribe: A$29 a monthNew in version 1.0.2 (30 Oct 2026): For construction work, the court rate it compares with the contract rate is now named as the court's rate after judgment, with the page that publishes it.
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Price details
- Price in Australian dollars (A$). Trilly isn't registered for GST, so no GST is added.
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- How buying works
- Sold worldwide.
- Charged every month until you cancel. Updates arrive by themselves.
- Updated 30 Oct 2026 · What's changed
- In your AI app: link once, then add it by asking. How