Invoicing basics
What is an invoice?
A plain-language definition of an invoice, the common types you'll come across, and the details that make one hold up in your records.
Key takeaways
- An invoice is a seller's formal request for payment for goods or services provided or agreed.
- It also serves as a record for bookkeeping, taxes, and resolving disputes.
- Common types include standard, recurring, interim, final, credit memo, and proforma invoices.
- Required details vary by country, so confirm local rules with an accountant or tax authority.
An invoice is a document a seller sends to a buyer to request payment. It lists what was provided, what it costs, and when and how payment is due. That's the short definition.
The longer answer is that an invoice is also a record both sides rely on, for bookkeeping, for taxes, and for settling any disagreement about what was agreed. Understanding that second role is what separates a quick note asking for money from an invoice that holds up months later.
What an invoice does
An invoice has three jobs. Each one shapes what belongs on the page.
- It requests payment. It tells the client the amount owed, the deadline, and the ways they can pay.
- It records a transaction. For the seller, an issued invoice is often the point at which revenue is recorded. For the buyer, it supports an expense or a purchase.
- It documents the terms. If a payment is late or a charge is questioned, the invoice is the reference point for what was sold, at what price, and on what terms.
In accounting terms, an unpaid invoice is an account receivable for the seller and an account payable for the buyer. When it's paid, both sides close it out. Whether revenue is recorded when you invoice or when you're paid depends on your accounting method, which is worth confirming with whoever does your books.
Invoices vs. other billing documents
Invoices are easy to confuse with the documents that come before and after them. For a typical business sale, the order runs like this:
- Estimate or quote: the expected price, sent before work begins. See how to write an estimate.
- Purchase order: the buyer's formal approval to buy, common at larger companies.
- Invoice: the request for payment, sent once goods or services are delivered or a milestone is reached.
- Receipt: proof that payment was received. The invoice vs. receipt guide covers the difference in detail.
Common types of invoices
Most businesses use a standard invoice most of the time. The other types exist for specific situations.
| Type | What it's for | Example |
|---|---|---|
| Standard | A one-time request for payment after delivery | A photographer billing for an event shoot |
| Recurring | The same charge on a regular schedule | A $450 monthly website maintenance plan |
| Interim (progress) | Partial payment during a long project | A contractor billing when framing is complete |
| Final | The closing invoice for a project, net of earlier payments | The last bill on a kitchen remodel |
| Credit memo | Reduces or reverses an amount already invoiced | A $120 credit for a returned item |
| Debit memo | Increases an amount already invoiced | Adding a shipping charge that was missed |
| Proforma | A preliminary invoice issued before delivery | A preview invoice for an export order |
| Timesheet | Billing based on hours worked | A consultant billing 22 hours at $140 per hour |
If you bill the same client the same amount every month, recurring invoices are worth automating so they go out on time without manual work. Proforma invoices follow their own conventions; see what a proforma invoice is for when to use one.
What a legally useful invoice typically contains
There is no single global standard. What's required depends on your country, sometimes your state or province, and whether you're registered for sales tax, VAT, or GST. That said, a well-made invoice usually includes:
- The word "Invoice" clearly displayed
- A unique, sequential invoice number
- The issue date and, where relevant, the date goods or services were supplied
- Your business name, address, and contact details
- The client's name and billing address
- A description of each item or service, with quantity and price
- The subtotal, any tax shown separately, and the total amount due
- Payment terms and the due date
- Your tax registration number, if your jurisdiction requires it
Some places add specific requirements, such as particular tax wording, the buyer's tax number for business-to-business sales, or rules for invoices issued in a foreign currency. Check with an accountant or your local tax authority for the rules that apply to you.
An invoice in practice
Consider a commercial cleaning company that services a dental office weekly. On October 31, it issues invoice CLN-0118 to the office manager. The invoice lists four weekly cleanings at $180 each, one window-cleaning add-on at $95, and a total of $815. It states Net 15 terms with a due date of November 15, shows the company's bank details and a card payment link, and references the service agreement signed in January.
Every element does a job. The number makes it traceable. The dates set the deadline. The line items let the office manager confirm the visits happened. The agreement reference ties the charges back to terms both sides already accepted.
Paper, PDF, or electronic
Most small businesses now send invoices as PDFs or as links to an online invoice, and both are widely accepted. Some governments are introducing structured e-invoicing requirements, particularly for business-to-business sales and work with public agencies. These systems use machine-readable formats rather than PDFs. If you sell into a country with an e-invoicing mandate, confirm the format your clients need before you bill them.
Creating your first invoice
Once you know what an invoice is for, making one is mostly a matter of getting the details right. Our step-by-step guide on how to make an invoice covers the process in order, and the free invoice generator lays out every field described above.