What is an invoice? A guide for small businesses

Published Thursday 9 July 2026

Table of contents

• What is an invoice?
• What to include on an invoice
• Common types of invoices
• Invoice vs. receipt vs. bill
• How the invoicing process works
• Understanding invoice payment terms
• How to handle late and unpaid invoices
• Modern invoicing methods
• Simplify invoicing with Xero
• FAQs on invoices

Key takeaways

• An invoice is a formal document requesting payment for goods or services that also serves as a legal record of the transaction between seller and buyer.
• Every invoice should include a unique invoice number, contact details for both parties, itemized line items, payment terms, and the total amount due.
• Understanding common invoice types, from standard and recurring invoices to credit notes and proforma invoices, helps you pick the right format for each transaction.
• Setting clear payment terms and following up on overdue invoices are 2 of the most effective ways to maintain steady cash flow.

What is an invoice?

An invoice is a document a seller sends to a buyer requesting payment for goods or services provided. It outlines what was sold, how much is owed, and when payment is due.

From the seller's side, this document is called a sales invoice. It's the record you create and send to your customer after delivering a product or completing a service. From the buyer's perspective, the same document is known as a purchase invoice, since it represents an amount they need to pay.

Invoices also play a key role in your accounting records. A sales invoice appears as an accounts receivable entry in your books, while a purchase invoice shows up as accounts payable. This distinction helps you track money coming in and going out with accuracy.

Beyond requesting payment, invoices serve as legal records of business transactions. They help you track income, manage cash flow, and maintain accurate financial records for tax purposes. If a dispute arises over a payment, the invoice acts as proof of what was agreed upon.

What to include on an invoice

A complete invoice gives your customer all the information they need to pay you on time. Here are the key components every invoice should have.

• Invoice number: A unique identifier that helps you and your customer track the transaction. Many small businesses use a sequential numbering system, for example, INV-001, INV-002, or a format that includes the year, like 2026-001.
• Invoice date and due date: The date you issued the invoice and the date payment is expected.
• Seller and buyer contact details: Full business names, addresses, email addresses, and phone numbers for both parties.
• Line items with descriptions, quantities, and prices: A clear breakdown of each product or service, including a brief description, the quantity provided, and the unit price.
• Payment terms: The conditions under which you expect payment, such as net 30 or due on receipt.
• Subtotal, tax, and total amount due: The sum of all line items before tax, any applicable sales tax, and the final amount your customer owes.
• Notes or special instructions: Any additional details, such as accepted payment methods, late payment fees, or a brief thank-you message.

Keeping your invoice format consistent makes it easier to organize records and locate specific transactions later. Choose a numbering system and layout that works for your business and stick with it. For a step-by-step walkthrough, see our guide on how to make an invoice. A professional, well-structured invoice also builds trust with your customers and reduces back-and-forth questions about what's owed.

Common types of invoices

Not every transaction calls for the same kind of invoice. Here are 8 common types you're likely to encounter as a small business owner.

• Standard invoice: The most common type, sent after delivering goods or completing a service. It includes all the usual details: line items, quantities, prices, and payment terms.
• Proforma invoice: An estimate or quote sent before work begins. Also known as a pro forma invoice, it outlines the expected costs but isn't a demand for payment. Once the buyer agrees, you follow up with a standard invoice.
• Recurring invoice: Used for ongoing services billed at regular intervals, such as monthly subscriptions or retainer agreements. The amount and details stay the same each billing cycle.
• Credit note: Issued when you need to reduce the amount a customer owes, for example, after a return, discount, or billing error. A credit note references the original invoice and adjusts the balance.
• Past-due invoice: A follow-up invoice or reminder sent when payment hasn't been received by the due date, also called an outstanding invoice. It typically restates the original amount and may include a late fee if your terms allow it.
• Commercial invoice: Used in international trade, this document accompanies goods shipped across borders. It includes details customs authorities need, such as the country of origin, harmonized system codes, and the value of the shipment.
• Interim invoice: Sent during a long-term project to bill for work completed so far. It allows you to collect partial payments at agreed milestones instead of waiting until the entire project is finished.
• Debit invoice: Issued when you need to increase the amount a customer owes, for example, if additional work was performed or costs were underestimated on the original invoice. It references the original invoice and adds the extra charge.

Invoice vs. receipt vs. bill

Invoices, receipts, and bills are related but serve different purposes. Knowing the difference helps you keep your records organized and communicate clearly with customers and vendors.

Invoice vs. receipt

An invoice requests payment before it's been made. You send it to a customer to let them know how much they owe and when the payment is due.

A receipt confirms payment after it's been made. Once your customer pays, you provide a receipt as proof that the transaction is complete.

Invoice vs. bill

A bill is essentially the same document as an invoice, just viewed from the buyer's side. When you receive an invoice from a supplier, you'd typically refer to it as a bill, since it's an amount you need to pay.

Invoice vs. purchase order

A purchase order is a document the buyer sends to a seller to formally request goods or services. It outlines what's being ordered, the quantities, and the agreed prices. An invoice, by contrast, is sent by the seller after the goods or services have been delivered, requesting payment for what was provided.

In short, a purchase order starts the transaction, and an invoice closes it. Both documents should reference each other for accurate record-keeping.

How the invoicing process works

The invoicing process covers every step from creating the invoice to recording the payment in your books. Here's how it typically works.

1. Create the invoice: Prepare a detailed invoice that includes all the required information: your contact details, the customer's information, line items, payment terms, and the total amount due.
2. Send it to the customer: Deliver the invoice by email, online invoicing software, or mail. Digital delivery is faster and creates an automatic record of when the invoice was sent.
3. Track payment status: Monitor whether the invoice has been viewed, is pending, or is overdue. Keeping tabs on payment status helps you follow up promptly if a due date passes. Xero Small Business Insights data shows late payment times for US small businesses improved throughout 2025, falling from 9.3 days late in Q1 to 7.8 days late in Q4, suggesting that consistent follow-up pays off.
4. Collect payment: Accept payment through the methods outlined on your invoice, such as bank transfer, credit card, or online payment. The easier you make it for customers to pay, the sooner you'll receive funds.
5. Reconcile in your records: Once payment arrives, match it to the corresponding invoice in your accounting records. This keeps your books accurate and gives you a clear picture of your cash flow.

Understanding invoice payment terms

Payment terms tell your customer when and how you expect to be paid. Setting clear terms upfront reduces confusion and helps you collect payments on schedule. Here are the most common ones.

• Net 30: Payment is due within 30 days of the invoice date. This is one of the most widely used terms for business-to-business transactions.
• Net 60: Payment is due within 60 days. This longer window is common for larger orders or when working with established clients.
• 2/10 net 30: The customer gets a 2% discount if they pay within 10 days; otherwise, the full amount is due within 30 days. This encourages early payment.
• Due on receipt: Payment is expected as soon as the customer receives the invoice. This is common for smaller transactions or when you need immediate cash flow.

Choosing the right payment terms depends on your industry, cash flow needs, and the relationship you have with each customer. Shorter terms bring money into your account sooner, while longer terms can help you win and keep clients. According to Xero Small Business Insights, US small businesses waited an average of 27.9 days to get paid in Q4 2025, with invoices paid an average of 7.8 days past the due date.

How to handle late and unpaid invoices

Late payments are a common challenge for small businesses, but having a clear process in place helps you recover what you're owed. Here's how to approach overdue invoices step by step.

Outstanding vs. unpaid invoices

An outstanding invoice is any invoice that hasn't been paid yet, whether or not it's past due. An unpaid invoice specifically refers to one where the due date has passed and payment still hasn't arrived. Understanding this distinction helps you prioritize which invoices need immediate attention.

Steps to follow up on late invoices

The sooner you act on an overdue invoice, the more likely you are to collect payment. Here's a practical approach.

1. Send a friendly reminder: A polite email or message the day after the due date can prompt payment without damaging the relationship. Include the invoice number, amount, and original due date.
2. Follow up with a formal notice: If the first reminder doesn't get a response within 7 to 14 days, send a more direct follow-up. Restate the amount owed and reference any late fee terms from the original invoice.
3. Pick up the phone: Sometimes a direct conversation resolves payment delays that emails can't. The customer may have a question about the invoice or be experiencing temporary cash flow issues.
4. Consider a payment plan: For larger amounts, offering a structured payment plan can help you recover the balance while maintaining the business relationship.
5. Escalate if necessary: If repeated attempts fail, you may need to involve a collections agency or seek legal advice. Document every communication so you have a clear record if the dispute escalates. For more strategies, read our guide on chasing outstanding invoices.

Preventing late payments

Setting up your invoicing process to minimize late payments saves you time and stress. Include clear payment terms on every invoice, offer multiple payment methods, and consider requesting a deposit upfront for larger projects.

Automated payment reminders can also make a significant difference. Xero customers who use online invoice payments get paid up to twice as fast. Enabling online payments and setting up automatic reminders can help keep cash flowing.

Modern invoicing methods

The way businesses handle invoicing has changed significantly. While paper invoices and PDF attachments still exist, many small businesses now rely on digital tools that simplify the entire process.

Online invoicing software lets you create, send, and track invoices from 1 place. Instead of manually formatting a document and emailing it as an attachment, you can generate a professional invoice in seconds and send it with a direct payment link.

The benefits go beyond convenience. Digital invoicing delivers invoices instantly, sends automatic payment reminders, accepts online payments, and gives you real-time visibility into which invoices are paid, pending, or overdue.

For small business owners, invoicing software eliminates repetitive admin work. You can set up recurring invoices, save customer details for future billing, and sync payments directly with your accounting records. Some platforms also offer AI-powered tools that can draft and send invoices on your behalf, reducing the manual effort even further.

E-invoicing is another growing trend. It refers to the electronic exchange of invoice data directly between accounting systems, without PDFs or paper. Several countries already require e-invoicing for certain transactions, and adoption is increasing in the US as businesses look for faster, more reliable ways to exchange billing information.

Simplify invoicing with Xero

Creating invoices, chasing payments, and keeping your books up to date takes time you could spend growing your business. Xero brings all of this into 1 platform so you can handle invoicing without the manual effort.

With Xero, you can create professional invoices in a few clicks, set up automatic payment reminders, accept online payments, and reconcile transactions as they come in. You can also request deposits on invoices, either as a percentage or a fixed amount, so you have cash in hand before work begins. Everything stays connected, so your cash flow picture is always current.

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FAQs on invoices

Here are answers to frequently asked questions about invoices.

What is the difference between an invoice and a receipt?

An invoice is sent before payment to request a specific amount for goods or services. A receipt is issued after payment to confirm the transaction is complete.

What does net 30 mean on an invoice?

Net 30 means the full invoice amount is due within 30 calendar days from the invoice date. It's one of the most common payment terms in business-to-business transactions.

What is a proforma invoice?

A proforma invoice is a preliminary document sent before goods or services are delivered. It outlines expected costs so the buyer can review and approve before committing, but it doesn't represent a final demand for payment.

When should you send an invoice?

Send your invoice as soon as the work is completed or the goods are delivered. The sooner you invoice, the sooner you start the payment clock.

Are invoices legally binding?

An invoice on its own isn't a contract, but it serves as evidence of an agreed-upon transaction. When paired with a signed contract or purchase order, it can support a legal claim for payment.

What is the difference between an invoice and a purchase order?

A purchase order is sent by the buyer to request goods or services, while an invoice is sent by the seller to request payment after delivery. The purchase order starts the transaction; the invoice closes it.