AnswersWhen a client won't pay
My client paid only part of the invoice. What about the rest?
The short answer
It is still owed. Say in writing, the same day, that it is part payment only, and ask for the balance by a date: interest at 8% over the Bank of England base rate5 keeps running on what is left, and the fixed sum (£40, £70 or £100, by size)3 is charged once. The payment also starts your six years again8 from the day it landed. An acknowledgement only counts if it is written and signed9; a payment needs no signature.
England and Wales only. WolfX is software, not a law firm.
What you can add
A £6,400 invoice, £4,000 paid 42 days late
Say you hired equipment to another business and invoiced £6,400, due on 14 August 2026. On 25 September, 42 days late, they pay £4,000 and nothing more. On 8 October the other £2,400 is still unpaid. Interest starts the day after the due date2, so on 15 August. The rate is set by the Bank Rate on 30 June 2026: 3.75%6 plus 8%5, or 11.75%.
- The invoice£6,400.00
- Less their payment on 25 September 2026−£4,000.00
- Interest to 25 September: £6,400 × 11.75% ÷ 365 × 42 days5£86.53
- Interest since, on the balance: £2,400 × 11.75% ÷ 365 × 13 days5£10.04
- Fixed sum (debts from £1,000 to £9,999.99)3£70.00
- Owed on 8 October 2026£2,566.57
Then it grows by £0.77 a day, on the £2,400, until they pay. Charging interest on the whole £6,400 right up to 8 October would overstate the total by £16.75.
The road ahead
Six steps. One court fee, if it comes to that.
Step 1: Read what came with the money
A note that names a fault with the invoice makes it a dispute: see what happens next. With no note it is just short, so ask: the letter below does.
A note saying "in full and final settlement" is an offer to close the debt for less. Tell them at once, in writing, that you do not accept it as settlement. Then read whether to accept less.
Step 2: Work out what is left
Work interest on the whole invoice up to the day the money landed, then on the balance1 from the next day. If it landed on or before the due date, interest only ever runs on the balance.
Add the fixed sum3 once. It arises once interest begins to run, so the band follows the debt interest started on: here the whole £6,400, so £70. The part payment does not earn a second one.
Step 3: Reply in writing the same day
Send the letter below. It thanks them, says which invoice the money went against and that it is part payment only, shows the balance with the working, and asks for a date.
Keep the original invoice number on the balance. GOV.UK says to send a new invoice4 when you add interest, so that one carries the interest and the fixed sum only.
Step 5: Give them 14 days, then send a letter before action
Your reply gives them 14 days. If it passes in silence, send a letter before action for the balance, interest and fixed sum. Sent one before the part payment? Then no second one and no new date: have the letter below name the day the claim starts, after that letter's date, and start it.
A company usually gets 14 days11 to answer it, a sole trader 3012. If they ask for time to pay the rest, read the payment plan page before you agree.
Step 6: Still unpaid? Claim the balance
The claim is for the balance, with interest and the fixed sum, not the whole invoice. A claim of £1,500.01 to £3,000, interest included, has a court fee of £11510. Here the claim is £2,566.57.
The court page takes you through the form.
A letter you can copy
Reply to a part payment: balance, interest and a date
Send it the day the part payment arrives, or today if days have passed, once you have read what came with it. It also answers a payment sent as a settlement offer.
Tap a highlighted gap to see what goes in it.
Send it by email the same day, so it is dated, and keep a copy with the invoice and whatever came with their payment. If they did not say which invoice the money was for, say which one you have applied it to. Work the first interest line to the day they paid and the second from the next day to today. The balance keeps its invoice number; the new invoice carries only the interest and the fixed sum. If they have named something wrong with the invoice, use the reply on the disputes page instead of this one. If you want to take less, read the page on accepting less before you send anything.
When not to bother
When it isn't worth it
- They are a consumer, or you are outside England and Wales. This page is for business customers in England and Wales. Consumer sales follow other rules, and Scotland and Northern Ireland have their own courts.
- The short payment matches a credit note you agreed. If their figure is your invoice less a credit you agreed in writing, nothing is owed. Check your records before you chase.
- They have told you in writing that part of the invoice is wrong. That part waits. Ask for the rest, work interest on the rest only for now, and follow what happens when a client disputes your invoice.
- The balance is small and the client is worth keeping. Interest on a few pounds is pence. Ask for the balance in one plain line, and decide whether to let the interest go.
- Six years had already run before the payment. A later payment does not revive a claim that is out of time8, so check the due date first.
The Wolf's note
Some of the money has moved, so the useful question is when the rest follows. Say in writing what the payment was and was not, and ask for the date. "Balance to follow" becomes a plan only when they name one.
Mr. Wolf · the AI inside WolfX
What comes next
Your next move
If they push back
Should I accept less in "full and final settlement"?
Only on your terms. In a small claim, turning down an offer is not, of itself, unreasonable behaviour, but treat any deal you agree as binding.
7 min read · Letter included
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
How long can I chase an unpaid invoice before it's too late?
Six years to start a court claim for an unpaid invoice in England and Wales, usually from the due date.
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.