Straight answer: invoicing a client the right way means putting the correct legal and payment details on the document, sending it the moment the work is finished (not “when you get a minute”), setting a clear due date instead of a vague one, and following up before the invoice is even late. Most late payments aren’t caused by difficult clients, they’re caused by invoices that were confusing, incomplete, or sent too casually to be taken seriously.
What “the right way” means
I’ve been invoicing clients for over two decades, across three countries and more currencies than I’d like to count, and the pattern never changes. The freelancers and small businesses who get paid on time aren’t the ones with the best work. They’re the ones with the clearest paperwork. An invoice isn’t just a bill, it’s an instruction to someone else’s accounts team, and if that instruction is unclear, it goes to the bottom of the pile.
Getting it right isn’t complicated. It’s a handful of habits, done every single time, without exception.
The bare minimum every invoice needs
Before you send another invoice, check it has every one of these:
- Your full business name and address (not just an email signature)
- The client’s full legal business name and address
- A unique invoice number that follows a logical sequence
- The invoice date and the payment due date, written as an actual date, not “30 days”
- A clear description of the work, including dates or a project reference
- The total amount, broken down by item if there’s more than one
- VAT details if you’re VAT registered, including your VAT number
- Your bank details or payment link
- Payment terms, including what happens if the invoice is late
That address line trips up more people than you’d think. I’ve written about this before, but it’s worth repeating: an invoice missing a proper business address can get bounced by an accounts department before anyone even looks at the amount owed, which is exactly why invoices need a proper address on them. It looks like a small formatting detail. It isn’t.
My £4,200 lesson in invoice numbers and PO references
Years ago I did a chunk of consulting work for a mid-size corporate client, roughly £4,200 worth over six weeks. I sent a clean, professional-looking invoice the day the project ended. No PO number on it, because nobody had mentioned one, and I hadn’t asked.
That invoice sat untouched in their system for eleven weeks. Not because the client was avoiding me, but because their accounts payable process couldn’t process anything without a purchase order reference attached. My contact had left the company two weeks after the project finished. Nobody chased it internally because, from their side, there was nothing to chase, it simply wasn’t in the queue at all.
I only got paid because I rang the finance department directly and asked what was missing. The answer was one line: “we need a PO number before this can go through.” One question at the start of the project would have saved me eleven weeks of chasing my own money. Now I ask every new corporate client, before I do a single hour of work, “do you need a PO number on the invoice?” It takes ten seconds and it has never once cost me a client to ask it.
When to send the invoice
Send it the same day the work or milestone is finished. Not the following Monday, not “when the invoicing pile gets big enough.” Every day you sit on an invoice before sending it is a day added to how long you’ll wait to get paid, because most companies count payment terms from the invoice date, not the completion date.
For longer projects, invoice in stages: a deposit before you start (I ask for 50% upfront on anything over a few thousand pounds), a milestone invoice partway through, and a final invoice on completion. Waiting until the very end to send one large invoice is the single most common reason small businesses run into cash flow trouble. You did the work months ago. You shouldn’t be financing your client’s project for free.
Setting payment terms that get you paid
Net 30 has become the default because it’s what everyone else uses, not because it’s a good idea for you. If you’re a small business or a freelancer, you’re essentially giving your client a 30-day interest-free loan every time you invoice on those terms. I moved most of my own invoicing to 14-day terms years ago, and new clients almost never push back. They’re used to accepting whatever terms are put in front of them, they just rarely get asked to accept shorter ones.
Here’s the part most invoicing guides won’t say plainly: generous payment terms don’t make you look accommodating, they make you look like someone who won’t chase the money, which trains slow payers to put you last. The clients I’ve worked with who take longest to pay are almost never the ones on 14-day terms. They’re the ones on 60 or 90-day terms, because there’s simply more room for the invoice to drift down the pile.
State your terms in plain language on the invoice itself: “Payment due within 14 days of invoice date. Late payments are subject to statutory interest under the Late Payment of Commercial Debts Regulations.” In the UK, you have a legal right to claim interest and compensation on overdue business-to-business invoices, and stating that right on the invoice, even if you never charge it, changes how seriously it gets treated.
Invoice or receipt, and why the difference matters
I still see business owners confuse these two documents, and it causes real problems at tax time. An invoice is a request for payment, sent before or at the point money changes hands. A receipt is proof that payment has already happened. Sending a client a “receipt” when you mean an invoice can create confusion about whether they’ve paid you at all, and I’ve seen it delay payment simply because the client’s accounts team assumed the balance was already settled. If you’re not sure which one you should be sending, this breakdown on whether it’s an invoice or a receipt, and whether it matters is worth five minutes of your time.
VAT, ad spend, and the small print people miss
If you’re VAT registered, your VAT number and the VAT amount charged need to be visible on every invoice, not buried in a footer. This gets messier when you’re invoicing clients for work that includes third-party costs, like ad spend. I get asked constantly by clients running paid campaigns whether platforms charge VAT the same way an agency invoice would, and the answer depends entirely on where the platform is registered and where your business sits. I broke this down when a client asked me about whether Facebook charges VAT on ad spend, because the answer changes what you should be showing on your own invoice to that client. Get this wrong and you either undercharge yourself or overcharge a client who then queries the whole invoice, which delays payment on everything, not just the VAT line.
Sending invoices the way your client wants them
Email with a PDF attached is still the standard, but a lot of smaller clients and international clients now expect quicker channels for confirmation, chasing, or sending a payment reminder. I use WhatsApp with several long-term clients purely to nudge them that an invoice has landed in their inbox, because a short message gets read faster than another email. If you’re using WhatsApp for business communication at all, it’s worth knowing exactly whether WhatsApp Business is free or has hidden charges before you build it into your invoicing workflow, because the free version has limits that catch people out once they’re relying on it daily.
Chasing payment without wrecking the relationship
Chasing an invoice is not rude. I’ve had newer business owners tell me they feel awkward following up, as if asking to be paid for finished work is somehow an imposition. It isn’t. Here’s the sequence I use, and it works with almost every client type:
- Day of due date: a short, friendly email. “Just flagging that invoice #1042 is due today, let me know if you need anything from me to process it.”
- 7 days overdue: a direct email restating the amount, the invoice number, and the original due date, no apology attached.
- 14 days overdue: a phone call, not another email. People are far quicker to act after a conversation than a third message sitting in an inbox.
- 21 days overdue: a formal notice referencing your right to statutory interest, sent to whoever manages accounts payable, not just your original contact.
The Federation of Small Businesses has reported for years that the average small UK business is owed thousands of pounds at any given time in late payments, and unpaid invoices are one of the most commonly cited reasons small businesses fail in their first few years, not lack of clients or lack of work. Chasing money isn’t a character flaw. Not chasing it is what sinks businesses.
What most people get wrong (and it’s usually not the client)
Here’s the uncomfortable part. When freelancers tell me a client “always pays late,” I ask to see the last invoice they sent. Nine times out of ten there’s a problem on their end: no PO number, no clear due date, an invoice number that doesn’t follow the last one, a vague description like “consulting services” with no dates attached. Accounts departments don’t process unclear paperwork quickly, whatever the size of the business behind it. Before you decide a client is a bad payer, check whether your own invoice gave them a reason to pay you promptly, or just something to set aside until it becomes urgent.
This is also where outsourcing your admin starts to pay for itself. If invoicing, chasing, and bookkeeping are eating hours every week that should be spent doing billable work, it’s worth treating it the same way you’d treat any other decision about whether outsourcing your website build is right for you, weigh the hourly cost of doing it yourself against the cost of handing it to someone who does it faster and gets it right the first time.
A simple invoice checklist before you hit send
- Correct business names and addresses on both sides, spelled exactly as registered
- A unique invoice number, higher than your last one
- Clear invoice date and due date, written as actual dates
- A specific description of work, with dates or project reference
- VAT number and VAT amount shown separately, if applicable
- Correct bank details, double-checked, not copied from an old template with an old account number
- PO number included, if the client’s process requires one
- Payment terms and late payment policy stated in plain language
Print that list, keep it next to your invoicing software, and run through it every single time until it becomes automatic. It takes ninety seconds and it will save you weeks of chasing.
Frequently asked questions
How long should I give a client to pay an invoice?
Fourteen days is a sensible default for most freelance and small business work. Thirty days has become the norm mainly because clients expect it, not because it benefits you, and shorter terms rarely get pushed back on if you state them clearly from the start of the working relationship.
What should I do if a client just ignores my invoice?
Move from email to a phone call once the invoice passes seven days overdue, and address the call to whoever handles accounts payable, not just your usual contact, since your invoice may simply be stuck in a queue rather than being deliberately ignored. If it passes twenty-one days, send a formal written notice referencing your legal right to statutory interest under UK late payment law.
Do I need to charge VAT on every invoice?
Only if you’re VAT registered, which in the UK becomes compulsory once your taxable turnover passes £90,000 in a twelve-month period, though you can register voluntarily below that threshold. If you’re registered, VAT must be shown clearly and separately on every invoice, along with your VAT registration number.
Is it unprofessional to ask about a PO number before starting work?
No, it’s the opposite. Asking whether a client needs a purchase order number before you start makes you look organised and experienced, not difficult. Skipping that question is what leads to invoices sitting unpaid for weeks because they can’t even enter the client’s payment system.
