To write an invoice, list your business details and your client's, give the invoice a unique number, add the invoice date and a due date, itemize the work with quantities, rates and amounts, show tax separately, and finish with the total, your payment terms and how to pay. Send it the day the work is done.
The rest of this guide walks through each part in order, shows a filled-in example with real numbers, and covers the mistakes that most often hold up payment. If you freelance, our guide to invoicing clients as a freelancer covers rates, milestones and follow-ups for solo work.
What must an invoice include?
An invoice needs enough detail for the client to approve and pay it without writing back to ask a question. Requirements differ by country. The UK government's invoice guidance lists these as required for UK businesses, and the same list works as a sensible baseline anywhere:
| Item | Required in the UK? | Why the client needs it |
|---|---|---|
| A unique invoice number | Yes | Their accounts team files and matches payments by it |
| Your business name, address and contact details | Yes | So they know who to pay and who to ask |
| The client's company name and address | Yes | Invoices go to the legal entity, not only your contact |
| A clear description of what you are charging for | Yes | Approvers sign off on what they can recognize |
| The date the work was done or goods supplied | Yes | Ties the charge to a period or delivery |
| The invoice date | Yes | Starts the clock on payment terms |
| The amounts charged and the total owed | Yes | The number they pay |
| Tax, shown separately | Yes, if you charge VAT | Lets VAT-registered clients reclaim it |
| A due date and payment terms | Not on the list, but include it | Without it, "when" is open to interpretation |
| How to pay | Not on the list, but include it | Every extra step delays the payment |
If you are registered for VAT, GST or a similar tax, your tax authority will expect extra details such as your registration number. Check its own guidance. The glossary entry on the tax invoice explains the difference, and our invoice requirements by country pages list the fields field by field, including the UK's VAT invoice rules, Australia's tax invoice rules and Canada's GST/HST invoice rules.
How do you write an invoice, step by step?
Work from the top of the page to the bottom. Each step below is one block on the invoice.
- Add a header that says "Invoice". Put your logo and business name at the top. The word "Invoice" should be the largest text, so nobody mistakes it for a quote.
- Add your business details. Your business name, address, email and phone number. Add your tax registration number if you have one.
- Add the client's details. The company's legal name, its billing address, and the name of the person or department who approves invoices. If the client gave you a purchase order number, add it here. Many accounts teams reject invoices without one.
- Give it an invoice number. Use a sequence that never repeats, such as INV-0041, INV-0042. Never reuse a number, even for a cancelled invoice.
- Add the dates. The invoice date, the date or period of the work, and the due date written out as a date, such as "Due October 27, 2026".
- List the line items. One row per service or product, each with a description, quantity, rate and line amount. A line item like "Website copy, 3 pages" gets approved faster than "Services rendered".
- Add the subtotal, tax and discounts. Show the subtotal, then any discount, then each tax as its own line with its rate.
- Show the total due. Make it the most visible number on the page and include the currency, such as USD 747.36.
- State your payment terms. For example, "Net 14" or "Due upon receipt", plus any late fee clause the client already agreed to.
- Explain how to pay. A pay-online link, bank details, or both. Add a short thank-you note at the bottom if you like.
The order matters less than completeness. An invoice missing the due date or the payment method is the one that sits in an inbox.
What does a finished invoice look like?
Here is a complete invoice from a small landscaping business, written with the 10 steps above.
INVOICE
Oak & Pine Landscaping, 14 Mill Road, Springfield. billing@oakandpine.example, (555) 010-2200
Bill to: Harbor View Apartments LLC, Accounts Payable, 200 Lake Street, Springfield. PO number: HV-1187
Invoice number: INV-2026-0042
Invoice date: October 13, 2026
Work completed: October 9 to 10, 2026
Due date: October 27, 2026 (Net 14)
| Description | Qty | Rate | Amount |
|---|---|---|---|
| Fall cleanup, front and rear beds (labor) | 6 hours | $65.00 | $390.00 |
| Hardwood mulch, delivered and spread | 4 cu yd | $48.00 | $192.00 |
| Hedge trimming, street frontage | 1 | $150.00 | $150.00 |
| Subtotal | $732.00 | ||
| Sales tax, 8% on mulch only | $15.36 | ||
| Total due (USD) | $747.36 |
Payment terms: Net 14. Payment is due by October 27, 2026.
How to pay: Pay by card or PayPal at the link on this invoice, or by bank transfer to the account below, quoting INV-2026-0042.
Thank you for your business.
A few details make this example easy to pay:
- The PO number is on it. The client's accounts team can match the invoice to an approved order without asking.
- The due date is a date. "Net 14" alone makes the client count. "October 27, 2026" does not.
- Tax is on its own line. Which items are taxable and at what rate depends on your state or country. The 8% here is only for illustration. Our guide to sales tax on labor and services covers the rules by trade.
- The payment reference is the invoice number. That makes the bank transfer easy to match when it arrives.
For trade-specific versions with sample line items and tax lines, see the industry pages for plumbers, electricians, contractors, cleaning businesses, landscapers and photographers.
How do you make an invoice for free?
You have three free options, and they all produce the same document:
| Method | Good for | Watch out for |
|---|---|---|
| Free invoice generator | A one-off invoice as a PDF in a few minutes | You keep your own record of invoice numbers |
| Word, Excel, Google Docs or PDF templates | Reusing the same layout each time | Totals and numbering are manual unless the spreadsheet does the math |
| A blank document | Full control over the layout | Easy to leave out a required field |
Templates and generators work well for a handful of invoices a month. Once you are tracking which invoices are paid, chasing the late ones and billing some clients every month, invoicing software does that bookkeeping for you.
What are the most common invoicing mistakes?
Most delayed payments trace back to one of these:
- No due date, or a vague one. "Payment due soon" gives the client nothing to schedule. Our guide to invoice payment terms explains the common options, from due upon receipt to net 30.
- Billing the wrong entity. Addressing the invoice to your contact rather than their company, or leaving off the PO number, sends it back for correction.
- Vague line items. "Consulting, $2,400" invites questions. "Strategy workshop, 2 days at $1,200" does not.
- Duplicate or skipped invoice numbers. They confuse your records and the client's, and a gap makes a missing payment harder to spot.
- No easy way to pay. If the client has to look up your bank details, the payment waits until someone has time.
- Sending it late. An invoice sent two weeks after the work starts the payment clock two weeks late.
When should you send an invoice?
Send the invoice the day the work is finished or delivered. For ongoing work, invoice on the same date every month so the client expects it. For large jobs, agree on a deposit and staged invoices before you start. Our guide to payment in advance covers deposits and upfront terms.
Is an invoice the same as a quote or a receipt?
No. Each document has a different job:
- A quote or estimate comes before the work and states the price you are offering. It does not ask for payment.
- A proforma invoice is a preliminary invoice sent before the work or delivery, often so the client can arrange payment or approval. It is not recorded as a sale in your books until the final invoice replaces it.
- An invoice comes after the work and asks for payment by a date.
- A receipt comes after payment and confirms the money arrived.
If you got the price wrong after sending an invoice, issue a credit note rather than editing the original.
Our guide to quote vs invoice vs receipt follows one job through every document in order.
How does invoicing software change the process?
Software fills in the steps you would otherwise repeat by hand. In SolidInvoice, your business details and logo are saved once, clients are stored with their billing addresses, and each line can carry its own tax rate and discount. When a client approves a quote, you mark it accepted and it becomes a draft invoice with every line copied over, so nothing is retyped. Every invoice has a pay link for card or PayPal, and you can download it as a PDF.
Once an invoice is out, SolidInvoice tracks whether it has been paid. On Pro and Business plans, it sends payment reminders on a fixed schedule after the due date. See the estimate software and invoice reminder pages for how each works, or pricing for what each plan includes.
How to write an invoice FAQ
What should an invoice include?
An invoice should include a unique invoice number, your business details, the client's business name and address, the invoice date, the date of the work, a description of each item with quantity and rate, any tax shown separately, the total due, the due date, your payment terms and how to pay.
Does an invoice need an invoice number?
Yes. Every invoice should have a unique number that is never reused. The client's accounts team uses it to file the invoice and match the payment. In the UK, GOV.UK lists a unique identification number as a required part of every invoice.
How do I make an invoice for free?
Use a free invoice generator or a template in Word, Excel, Google Docs or PDF. Fill in your details, the client's details, an invoice number, dates, line items, tax and the total, then download it as a PDF and email it. Keep a list of the numbers you have used so none repeat.
When should I send an invoice?
Send an invoice the day the work is finished or delivered. Payment terms start from the invoice date, so every day you wait pushes the payment back by a day. For ongoing work, invoice on the same date each month.
What is the difference between an invoice and a receipt?
An invoice asks the client to pay and states when payment is due. A receipt confirms that payment has been received. You send the invoice first, and the receipt after the money arrives.
Can I write an invoice in Word or Excel?
Yes. A Word or Excel invoice is valid as long as it includes the required details, such as an invoice number, dates, line items, tax and the total. Send it as a PDF so the client cannot edit it and the layout looks the same on every device.
Save your details once, put a pay link on every invoice, and see which ones are still unpaid. Start a free 14-day trial of SolidInvoice.