How to make an invoice: a step-by-step guide

You finished the work, and now you need to get paid. This guide walks through how to make an invoice from start to finish: first with KeenInvoice, then in general terms if you prefer another tool, followed by what to include, how to send it, how to follow up, and the mistakes that most often delay payment.

Before you start

Gather a few things so you can fill in the invoice in one go:

• Your business name, address, email, and any tax ID you are required to show.
• Your client’s legal or trading name, billing address, and the person or department who handles payments.
• A purchase order (PO) number, if the client gave you one.
• What you supplied: products or services, quantities or hours, and agreed prices.
• The payment terms you agreed, and how you want to be paid.

If you’re not sure what an invoice needs to contain, our guide to what an invoice is covers each part.

How to create an invoice with KeenInvoice

KeenInvoice runs in your browser, saves as you type, and doesn’t ask you to sign up. Here’s the whole process.

1. Open the invoice generator

Go to the invoice generator. There is nothing to install and no account to create; you start typing straight away, and your work is saved in your browser as you go.

2. Add your business details and logo

Enter your name or business name, address and contact details. Upload your logo if you have one. You only do this once: when you click New later, your details, logo, currency, tax settings, payment details and design carry over to the next document.

3. Add your client

Type the client’s name and billing address. Add a ship-to address if goods are going somewhere else. After your first few invoices, client names autocomplete from your past documents.

4. Check the invoice number and dates

Make sure the invoice number is unique and follows on from your last one. KeenInvoice counts on automatically (INV-0009 is followed by INV-0010), but you can type any number you like. Set the invoice date to the date you issue it.

5. Choose payment terms

Pick Due on receipt, Net 7, 14, 15, 30, 45, 60 or 90, End of month, or a custom term. The due date is calculated for you, so it is always printed on the invoice.

6. Add line items

For each product or service, enter a clear description, the quantity (or hours), and the unit price. The line totals and subtotal update as you type. Items you’ve used before autocomplete too. If you bill by the hour, the hourly invoice template is set up for hours and rates.

7. Add tax, discounts and shipping

Choose no tax, one rate on the total, or a rate per line (useful when items are taxed differently). You can rename the tax to VAT, GST or sales tax, and mark prices as tax-inclusive if that is how you quote. Add a discount or shipping if needed. If the client has already paid a deposit, enter it as the amount paid and the invoice shows the balance due.

8. Add payment details and notes

Tell the client exactly how to pay: bank details, accepted methods, and what reference to use. Add the PO number, a short thank-you, or your terms and conditions. Custom fields are there for anything else, such as a project code.

9. Choose a design and download

Pick a design (Classic, Modern, Minimal or Japanese), an accent color and paper size (A4 or US Letter). If your client works in another language, switch the document language to English, Japanese, Spanish or German. Then download the PDF or print it.

Your invoice stays saved in My documents, where you can mark it as sent and later as paid.

Making an invoice in Word, Excel or Google Docs

You can absolutely make an invoice in a word processor or spreadsheet, and plenty of people do. The trade-offs are worth knowing:

• Word or Google Docs give you full control over the layout, but you do the math yourself, and it is easy to forget to update a total after changing a line.
• Excel or Google Sheets handle the calculations with formulas, but the layout takes effort to get right, and a broken formula can go unnoticed.
• With either, you manage numbering, file names and paid/unpaid status by hand. The most common slip is copying last month’s file and forgetting to change the number or date.

At the other end, full accounting software makes sense if you need payment collection, automatic recurring invoices, bank reconciliation or e-invoicing. A dedicated generator like KeenInvoice sits in between: fast and free for making correct documents, without the extras.

What to include on every invoice

Whatever tool you use, check for these before sending:

• The word “Invoice” and a unique invoice number
• Invoice date and due date
• Your details and your client’s details
• Clear line items with quantities, prices and amounts
• Subtotal, tax (with the rate), and total due
• Payment terms and payment details
• A PO number or reference, if the client uses one

Some places require more. In the EU and UK, for example, a VAT invoice must show the supplier’s VAT number, the VAT rate and the VAT amount. In some countries, such as Italy, Mexico and Brazil, business invoices must go through a government e-invoicing system, which a PDF does not replace. Check the rules where you work.

Numbering your invoices

Use a unique, sequential number for every invoice, in a consistent format such as INV-0001 or 2026-001. Never reuse a number, even for a cancelled invoice. Our guide on how to number invoices covers formats, gaps and voided invoices.

Setting payment terms

Agree payment terms before you start the work, and put them on the invoice along with an actual due date. Net 30 (payment due 30 days after the invoice date) is common between businesses, but shorter terms are fine and often sensible for freelancers. For a full rundown, see what Net 30 means.

Sending the invoice

KeenInvoice doesn’t send email, so you send the PDF yourself, which also means it comes from your own address. A few habits help:

• Send it promptly. The sooner it goes out, the sooner the clock on the due date starts.
• Send it to the right person. In larger companies that is often an accounts payable inbox, not your day-to-day contact. Ask if you’re not sure.
• Make it easy to find. Put the invoice number and your business name in the subject line and file name, for example “Invoice INV-0042 from Northwind Studio”.
• Say what’s attached and when it’s due in a line or two in the email body.

Following up

Most late payments are oversights rather than refusals, so a polite reminder usually works. A simple schedule:

1. A few days before the due date, a friendly note that the invoice is coming due.
2. On the due date, a short reminder with the invoice attached again.
3. A week or so after, a firmer follow-up asking when payment will be made.

Keep each status up to date in My documents so you can see at a glance what is overdue. If you charge late fees, they should be in your agreed terms from the start, and the rules on them vary by country and state.

Common mistakes to avoid

• Duplicate or missing invoice numbers. They confuse both sides and can cause problems in an audit.
• Vague descriptions. “Services” invites questions; “Logo design, three concepts and two rounds of revisions” doesn’t.
• No due date. “Payment due on completion” leaves the date open to interpretation. Print the date.
• Wrong client details. Use the client’s correct business name and include their PO number if they gave you one; otherwise the invoice may sit unapproved.
• Math errors. Let a calculator, spreadsheet or generator do the totals.
• Missing payment details. If the client has to ask how to pay, payment is already delayed.
• Editing an invoice after sending it. If something was wrong, issue a credit note and a corrected invoice with a new number.
• Waiting weeks to invoice. The longer you wait, the longer you wait to get paid.

Make your first invoice now

The quickest way to put all of this into practice is to fill in the invoice generator. It guides you through every part, does the math, sets the due date from your payment terms, and gives you a clean PDF without a sign-up or a watermark.