How to invoice as a consultant (US)

How consultants normally break the money out

A consultant's invoice is usually a day rate or fixed project fee, with reimbursable expenses billed at cost against the engagement letter. Keeping those apart is what stops the customer asking what the total covered.

Step by step

1. 1Quote the engagement letter or statement of work reference and the client's PO number. Invoices without a PO are the most common reason payment slips a month at a mid-size company.
2. 2Bill fees and reimbursable expenses on separate lines. Clients approve fees against the SOW and process expenses under a different policy.
3. 3Show the basis — days at a day rate, hours at an hourly rate, or a milestone of a fixed fee — and the period covered.
4. 4Send to accounts payable, not only to your day-to-day contact, and match their invoice format requirements exactly.
5. 5State your payment terms and where you accept ACH. Getting paid by ACH rather than check typically removes a week.

When to send it

Monthly in arrears for ongoing engagements, or on milestone completion for fixed-fee projects. Invoice before the client's month-end AP cut-off, not after.

At a corporate client, late payment is almost always a process problem, not a refusal. Ask AP for the invoice status and the scheduled payment run, quoting the PO number.

Common questions

Will my client need a W-9 and send a 1099?

US business clients generally require a W-9 up front and issue a 1099-NEC for the year if you are paid $600 or more. Send the W-9 with your first invoice.

Should I charge a late fee?

You can where your contract states it and state law permits the rate. State it in the engagement letter, not for the first time on the invoice.

Day rate or hourly?

Day rate for on-site and workshop work, hourly for advisory. State which and the number of units on the invoice.