What Is an Invoice? Meaning, Types and an Example

An invoice is a document a seller sends to a buyer to ask for payment for goods or services. It lists what was supplied, the price of each item, the total owed, and when and how to pay. For the seller it is a payment request and a record of income; for the buyer it is a record of what they owe and, later, of what they paid for.

If you have just started freelancing or selling, invoices can feel like paperwork you would rather skip. They are worth getting right: a clear invoice gets paid faster, settles disputes before they start, and is the document your accountant and the tax office will want to see.

What is an invoice used for?

An invoice does three jobs at once:

• It asks for payment. It tells the client exactly how much to pay, by when, and how (bank transfer, card, PayPal and so on).
• It is a record for both sides. The seller uses it to track income and unpaid work; the buyer's accounts team uses it to approve and log the expense.
• It is evidence. Tax authorities treat invoices as supporting documents for the figures on your return. The IRS, for example, lists invoices among the records that back up your business income and expenses.

How invoicing works, step by step

What goes on an invoice?

Requirements differ from country to country (more on that below), but a complete, professional invoice includes:

Invoice example

Here is what a simple invoice from a freelance designer to a client looks like, laid out as a table:

Below the total, the invoice would give the bank details for payment and a short note such as "Thank you for your business". To make your own, start from a ready-made graphic design invoice in the free editor, change the details and download it as a PDF. No sign-up is needed.

Invoice vs receipt vs bill vs quote

These four documents get mixed up all the time. The difference is when each one is used and who sends it:

The short version: a quote says "this is what it will cost", an invoice says "please pay this", and a receipt says "thank you, you've paid".

Types of invoices

Most small businesses only ever need the first one, but these are the names you will come across:

• Standard (sales) invoice: the everyday invoice for goods or services already delivered.
• Pro forma invoice: a preliminary invoice sent before delivery, so the buyer can arrange payment or approval. It is not a demand for payment and is not recorded as a sale.
• Interim (progress) invoice: bills part of a long project, for example at each milestone.
• Final invoice: closes a project, often after interim invoices, showing what has already been paid and the balance left.
• Recurring invoice: the same amount billed on a schedule, such as a monthly retainer or subscription.
• Timesheet invoice: bills hours worked at an hourly rate, common for contractors and consultants.
• Credit note (credit memo): reduces or cancels an earlier invoice, for example after a refund or an overcharge.
• Debit note: adds to an earlier invoice, for example when extra work was done.
• Past-due invoice: an invoice re-sent after the due date, usually with a reminder and any agreed late fee.
• Commercial invoice: used when shipping goods internationally; customs use it to assess duties.
• VAT invoice: an invoice that meets the extra VAT rules in the UK and EU, needed when both you and your customer are VAT registered.

What is an invoice number?

An invoice number is a unique reference given to each invoice so it can be tracked, paid and found again later. When a client pays, they quote it in the payment reference; when your accountant reconciles your books, they match payments to it.

The rules are simple: every invoice gets its own number, numbers go up in order, and you never reuse or skip one without a reason (a cancelled invoice is corrected with a credit note, not deleted). Common formats are:

• Sequential: INV-0001, INV-0002, INV-0003
• Year-based: 2026-001, 2026-002, which restarts the count each year while staying unique
• Client-based: NW-001 for Northwind, AC-001 for Acme, handy when you bill a few regular clients

Simple Invoice Generator numbers your invoices automatically and lets you set your own prefix in Account settings.

What must an invoice legally include?

There is no single worldwide rule, so check the requirements where you are registered. A few common examples:

• United Kingdom: every invoice needs a unique number, your name or company name and address, your customer's name and address, a clear description of what you are charging for, the supply date, the invoice date, the amounts and the total owed. Sole traders using a business name must also show their own name and an address for legal documents; limited companies must use the full name on their certificate of incorporation. If you and your customer are both VAT registered you must issue a VAT invoice, normally within 30 days of the supply; for sales of £250 or less (including VAT) a simplified VAT invoice is allowed.
• European Union: the EU VAT Directive (Article 226) sets out the details a VAT invoice must show, including both parties' VAT numbers where applicable. Each country adds its own rules, and several are moving to mandatory e-invoicing, so check your national tax office.
• United States: there is no federal invoice format, but the IRS expects you to keep records that support your income and expenses, and invoices are one of the main ones. Sales tax rules are set by each state.

This section is general information, not legal or tax advice. If you are unsure what applies to you, ask an accountant or your tax office.

When should you send an invoice?

As soon as the work is delivered, or as soon as a milestone is reached. Invoicing the same day is one of the easiest ways to get paid faster: the work is fresh in the client's mind and the payment clock starts sooner. Your payment terms tell the client how long they have. Net 30 (payment due within 30 days) is the most common for businesses, while Net 15 or "due on receipt" suit smaller jobs. Our guide on how to create an invoice online explains payment terms and follow-ups in more detail.

How to make an invoice

You can make an invoice in Word or a spreadsheet, but an invoice generator does the numbering, the maths and the PDF for you. With Simple Invoice Generator:

• Open the editor and fill in your details and your client's. No account is needed to try it.
• Add each item with a quantity and rate. The totals, tax and discount calculate themselves.
• Set the invoice date and the due date.
• Download the PDF, or create a free account to email it to your client with the PDF attached and track when it's paid.

Prefer to start from an example for your line of work? There are ready-made templates for graphic designers, photographers, web developers and consultants, plus a free Excel and Google Sheets invoice template.

Frequently asked questions

Is an invoice the same as a bill?
They describe the same document from opposite sides. The seller sends an invoice; the buyer receives it and usually calls it a bill. In everyday use the two words are interchangeable.

Does an invoice mean I have been paid?
No. An invoice is a request for payment, so it is issued before the money arrives. Once the client pays, you mark the invoice as paid and, if they ask, give them a receipt.

What is the difference between an invoice and a receipt?
An invoice asks for payment and shows what is owed and when it is due. A receipt confirms that payment has already been made. The invoice comes first, the receipt comes after.

Can I send an invoice if I am not a registered company?
Yes. Freelancers and sole traders invoice under their own name all the time. In the UK a sole trader must show their name and any business name they use, plus an address where legal documents can be delivered. Registering for VAT or sales tax is a separate question that depends on your turnover and where you work.

What happens if an invoice is not paid?
Start with polite reminders after the due date; most late invoices are simply forgotten. If you agreed late fees in your terms you can apply them. In the UK, businesses can also claim statutory interest on late business-to-business payments at 8% plus the Bank of England base rate, unless the contract sets a different rate.

How long should I keep invoices?
Keep copies of every invoice you send and receive, because they back up the income and expenses on your tax return. In the US the IRS generally asks you to keep records for 3 years (longer in some cases). UK sole traders must keep records for at least 5 years after the 31 January filing deadline for the tax year.