Handbook / Invoicing and getting paid

How to invoice clients: what goes on the page and when to send it

An invoice is the moment work turns into money. It is also a record you may need years later. A clear invoice gets paid faster because the client's accounts person does not have to ask questions, and a well-filed one supports your tax return without any extra effort. This guide covers what goes on the page, when to send it, and what to do with your copy.

The fields every invoice needs

US law does not prescribe a universal invoice layout for a sole proprietor's services, but some fields are effectively required because without them the invoice cannot be processed or filed. Put these on every invoice:

• Your details. Legal name or registered business name, address or business email, and phone if you use one for work.
• The client's details. Business name, the contact who approved the work, and their billing address or email.
• Invoice number. Unique and never reused.
• Issue date. The date you send it.
• Description of the work. What was delivered, matching the language of the agreed scope. Reference a purchase order or project name if the client uses one.
• Quantities and rates. Hours and hourly rate, or the fixed fee, or each line item.
• Total due. With any deposit already paid shown as a deduction.
• Due date and terms. For example, "Due within 14 days of the invoice date."
• How to pay. The methods you accept and the details needed for each.

Some clients also ask for your taxpayer identification on a Form W-9, which is a separate form, not part of the invoice. Do not put your Social Security number on an invoice.

Numbering that never repeats

Pick a scheme and stick to it. Simple sequential numbers work: 1001, 1002, 1003. Some people add the year: 2026-001. What matters is that each number is used once, in order, and that you can find any invoice by its number.

Record each number in your ledger as you issue it, along with the client, amount, and due date. If you void an invoice, keep it marked "void" rather than deleting it, so the sequence has no unexplained gaps.

When to send it

The best time is as soon as the agreed trigger happens. Common triggers:

1. On acceptance of a deliverable. For project work.
2. On a milestone. For longer projects split into stages.
3. On a set date. For retainers or monthly hourly work, for example the first working day of each month.
4. Before work starts. For deposits, if your terms require one.

Agree the trigger in writing before work begins, so the invoice is expected rather than a surprise. Payment terms such as "due in 14 days" usually run from the invoice date, so every day you wait to send it is a day added to when you get paid.

Writing payment terms people follow

Terms should be short, specific and identical every time. Name the period, the methods, and what happens if payment is late, in line with what you agreed in your contract.

Example terms line: Payment due within 14 days of the invoice date by bank transfer or card. A late fee applies as set out in our agreement of 3 March.

Do not invent a late fee on the invoice that was never agreed. If you want one, put it in the agreement first. Our working-alone guide on late payments covers what to do when an invoice goes past due.

A worked invoice

Here is how the fields come together for an invented job.

Invoice 2026-014. From: Rivera Editorial, [email protected]. To: Lakeside Dental, attention Sam Ortiz, [email protected]. Issued 4 November 2026. Project: patient newsletter, autumn issue, per agreement dated 6 October. Copyediting of eight articles, fixed fee $600. Less deposit received 6 October: $200. Total due: $400. Due by 18 November 2026. Pay by bank transfer (details enclosed) or card via the payment link.

Every number can be traced to the agreement, and anyone in the client's office can process it without asking a question.

Your copy is a tax record

The IRS lists invoices among the supporting documents that show the amounts and sources of gross receipts, alongside bank deposit slips, receipt books and Forms 1099-NEC. It recommends keeping supporting documents organized, for instance by year and type of income or expense, and in a safe place.

So file each invoice the day it is sent, in a folder by year, and mark it paid with the date and method when the money arrives. Match payments to invoice numbers in your ledger. At year end, your list of paid invoices should reconcile with your bank deposits; if it does not, find out why before you file.

For how long to keep them, the IRS's general rule is 3 years from the date you filed the return, with longer periods in some cases: 6 years if you did not report income that was more than 25% of the gross income shown, and indefinitely if you did not file or filed fraudulently.

Mistakes that slow payment

• Sending to the wrong person, or to a general inbox nobody watches.
• Vague descriptions such as "services rendered".
• Missing purchase order numbers when the client uses them.
• Totals that do not match the agreed price, with no explanation.
• No due date, or a due date that conflicts with the contract.

The habit that makes it work

Set a weekly ten-minute slot. Send any invoices that are due, record payments that arrived, and note anything overdue. A complete invoice sent on time and filed the same day does two jobs: it gets you paid and it proves what you earned.