Updated October 13, 2026
An invoice is a document a seller sends to a customer to request payment for goods or services. It lists what the customer is being charged for, the prices, the amount due, the payment deadline and how to pay.
In simple terms, an invoice says: “Here is the work or order, here is the cost, and here is when payment is due.” It can show a deposit or other payment already received, but issuing an invoice does not confirm that the customer has paid.
Invoice meaning and definition
An invoice gives both sides a record of a specific sale or service. The seller uses it to explain the charge and request payment. The customer uses it to check the goods or work, approve the amount and identify which payment to make.
For example, after completing a logo design, a freelancer sends the client an invoice for the agreed fee. A shop can invoice a product order, and a consultant can invoice the hours worked during a billing period.
What is an invoice in accounting?
An unpaid sales invoice helps a seller track money customers owe, usually called accounts receivable. The same document is a purchase invoice for the buyer and helps track money owed to a supplier, usually called accounts payable. The document is the same; the business's role is different.
Creating an invoice and recording a payment are separate steps. Keep the invoice, the payment record and any adjustment together so you can explain what was billed and what remains unpaid.
What does an invoice look like? A simple example
This fictional invoice uses the same kind of service lines shown on CatInvoice's homepage. Northstar Studio is billing Cedar & Co. in US dollars.
- Invoice number: INV-2026-0042
- Invoice date: October 13, 2026
- Payment terms: Net 15
- Due date: October 28, 2026
| Description | Quantity | Rate | Amount |
|---|---|---|---|
| Design refinements | 2 hours | $75 | $150 |
| Social graphics | 3 deliverables | $50 | $150 |
- Subtotal and total: $300
- Amount already paid: $100 deposit
- Balance due: $200
No tax, discount or shipping is included in this example. The calculation is $150 + $150 = $300, then $300 − $100 = $200 left to pay.
The payment note could say: “Please pay the remaining $200 by October 28, 2026 using the agreed bank transfer details. Include INV-2026-0042 as the payment reference.” Use your own agreed payment method and details.
In CatInvoice's free invoice generator, enter the two line items and the $100 in Amount paid. Check that the preview shows a $300 total and $200 balance before downloading the PDF.
What should you include on an invoice?
A useful invoice answers who is billing, what is being billed, how much is due and when to pay. Start with these details:
- Seller details: your business name or name, address and contact information.
- Customer details: the client or business name and the billing information they request.
- Invoice number: a unique reference for this document.
- Invoice date: the date you issue it.
- Due date and terms: the agreed deadline and any deposit or milestone arrangement.
- Line items: recognizable descriptions, quantities, rates and amounts.
- Currency and totals: the subtotal, applicable tax or VAT, discounts, shipping and total.
- Payments received: the amount already paid and the remaining balance.
- Payment instructions: the agreed method, details and payment reference.
- Order or project reference: a purchase-order number or job reference if your client needs it.
Describe the work clearly. “Logo design for October product launch” is easier to recognize than “Design work.” For hourly billing, include the hours and rate; for a fixed project, use the agreed project amount.
These are practical invoice essentials. Additional business, tax or registration fields depend on where you operate and the transaction. Check the requirements that apply to your own business.
What is an invoice number?
An invoice number is a unique identifier, such as INV-2026-0042. It helps you find the document, match a payment and discuss a specific bill with the customer. Keep a consistent numbering system and avoid reusing the same number for different invoices. CatInvoice lets you enter a custom invoice number.
Invoice vs receipt vs quote: what is the difference?
| Document | Purpose | Example |
|---|---|---|
| Quote or estimate | Propose a price or scope before the customer agrees. | A proposed $300 design project. |
| Invoice | Request payment under the agreed billing schedule. | A $300 invoice showing a $100 deposit and $200 due. |
| Receipt | Confirm payment was received. | Confirmation of the customer's $200 payment. |
Is an invoice a bill? In everyday use, both words can describe a payment request. Businesses often use “invoice” for the itemized document sent to a customer and “bill” for a charge they need to pay.
An invoice can also show that it has been paid. Confirm the actual payment before changing its status or amount paid; editing a document does not verify a bank transfer.
What is an open invoice?
An open invoice has been issued and still has money left to pay. An invoice with a $300 total and a $100 deposit remains open for the $200 balance. If the remaining payment passes the due date, the invoice is overdue.
For a plain explanation of this term, see Stripe's guide to open invoices.
In CatInvoice, update the amount paid after confirming a payment. Keep your own payment records and follow-up routine; the editor does not check bank transactions or send automatic reminders.
Common types of invoices
- Standard invoice: a payment request for a sale or completed service.
- Deposit invoice: a request for an agreed advance payment.
- Milestone or progress invoice: billing for a completed stage of a larger project.
- Recurring invoice: repeated billing for ongoing work, such as monthly consulting.
- Final invoice: the last bill for a project, accounting for earlier invoices and payments.
- Pro forma invoice: a preliminary document showing proposed transaction details before the final invoice.
A credit note is a related document used to reduce or correct an earlier invoice, rather than request a new payment.
These describe billing arrangements, not a list of CatInvoice automation features. For repeat work, you can duplicate a saved CatInvoice invoice, then review the new number, dates, items and payments. Recurring invoices are not automatically scheduled or sent.
When should you send an invoice?
Use the billing schedule agreed with your client: before starting for a deposit, after an approved milestone, after delivery, or at the end of a billing period. Check who receives invoices and whether a purchase-order reference is needed.
Write the actual due date as well as the payment term. Net 15 normally means payment is due 15 days after the invoice date. For the October 13 example, that is October 28. See the invoice payment terms guide for Net 7, Net 15 and Net 30 examples.
How to create a free invoice with CatInvoice
CatInvoice is a free, manual invoice editor for freelancers and small businesses. You can create and download a PDF without signing up or adding a CatInvoice watermark.
- Open the invoice editor and add your business and customer details.
- Set the invoice number, currency, invoice date and due date.
- Enter the goods or services, quantities and rates. Add applicable tax or VAT, discounts and shipping.
- Enter payments already received and add your payment instructions in the notes or terms.
- Choose a template, add your logo if needed, and review the live invoice preview.
- Download the PDF or print it. Attach the downloaded PDF using your own email or messaging app.
You can reuse saved clients and services and duplicate saved invoices for future work. Records stay in the current browser without automatic account sync. Export a JSON backup before clearing browser data or moving devices; a CSV history export is useful for summaries, but is not the full backup.
For a complete walkthrough, follow the CatInvoice invoice tutorial or browse free invoice templates.
Frequently asked questions about invoices
What does invoice mean in simple words?
An invoice is a payment request showing what a customer is being charged for, how much is due and when to pay.
Does an invoice mean the customer has already paid?
No. An invoice requests payment and can show an unpaid balance. A receipt confirms payment received. An invoice may also record a deposit or be marked paid after payment is confirmed.
What is an invoice number used for?
It identifies one invoice so you can organize records, match payments and refer to the correct document when talking with a customer.
What is the difference between an open and overdue invoice?
An open invoice has an unpaid balance. It becomes overdue when that balance remains unpaid after the due date.
Can I make an invoice for free without an account?
Yes. CatInvoice lets you enter invoice details, choose a template and download a PDF without an account or CatInvoice watermark.
Where does CatInvoice save my invoices?
Drafts and saved records stay in the browser on your device. Export a JSON backup to keep a portable copy and restore it in another supported browser.