How to Invoice as an Accountant
What goes on an accountant's invoice, in what order, on what terms, and how to follow up, with one worked example you can check line by line.
An accountant's invoice has to match the engagement letter: the client should be able to read each line and find the service it pays for. This guide goes through it in order: agree on the scope and fees, set up the invoice, bill fixed and hourly work on separate lines, then send it and follow up.
The Occupational Outlook Handbook from the US Bureau of Labor Statistics (last modified October 29, 2026) describes the work: "Accountants and auditors prepare and examine financial records." It adds: "Overtime hours are typical at certain periods of the year, such as for quarterly audits or during tax season." Set your invoicing routine up before those peaks arrive.
Worked example (sample figures; sales tax isn't included, so check your state's rules): a small business client pays a monthly bookkeeping retainer of 600.00. In March you also held a 2.5-hour advisory call at 150.00 an hour, which comes to 375.00, and the client agreed in writing to an amended return outside the engagement for a flat 250.00. The March invoice has three lines: 600.00 + 375.00 + 250.00 = 1,225.00.
Step-by-step invoicing guide
- 1
Agree on the scope and fees in the engagement letter
Before work starts, put the services, the fee for each (fixed, monthly or hourly) and your payment terms in the engagement letter. Every invoice line should point back to one of those services.
- 2
Set up the client and invoice details
Add the client's legal name and billing contact, an invoice number, the issue date and a due date. Billed's invoice software page says: "Set a due date on each invoice so your client knows when to pay."
- 3
Bill fixed fees and hourly work on separate lines
Give the monthly retainer, any fixed-fee return and any hourly advisory time a line each, with the month or date it covers. When you add the line, Billed's help center tells you to "fill this section to charge against new items and services."
- 4
Show the hours behind advisory work
For hourly work, list the date, topic and hours of each session. Billed's time tracking page says: "Create an hourly rate project, set its hourly rate, and Billed tracks the charge for each task as you log it."
- 5
Add out-of-scope work once the client agrees to it
Amended returns, extra state filings or added advisory calls go on a separate line after the client has agreed to the added fee in writing. Name what was requested and when.
- 6
Send the invoice and follow up
Send the invoice when the deliverable goes out, not weeks later. Billed's invoice software page says you can "Create branded invoices, send them by email, take card and PayPal payments on them, and see which invoices are paid, partly paid or past due, all from one Billed account."
Tips for accountant invoicing
- Put the engagement letter's date or reference in the invoice notes. Billed's help center says of the invoice notes: "You can also add any terms and conditions in this section."
- Write the month or quarter into each line description, so the client can file the invoice against the right period.
- Business clients may ask for Form W-9 before they pay you. The IRS page About Form W-9 (dated June 27, 2026) gives its purpose: "Use Form W-9 to provide your correct Taxpayer Identification Number (TIN) to the person who is required to file an information return with the IRS".
- For monthly retainers, Billed's invoice software page says: "For clients you bill on a schedule, set up a recurring profile once." It also says: "Choose the billing frequency (daily, weekly, monthly or yearly) and how many invoices to send, or keep sending until you stop."
- Use the payment terms from the engagement letter (for example, due in 15 or 30 days) on every invoice, so the two match.
Common invoicing mistakes to avoid
- One line for the whole month, so the client can't match the charge to the engagement letter.
- No period on the invoice, so the client can't tell which month or quarter the fee covers.
- Billing extra work the client didn't agree to in writing.
- Waiting until after tax season to bill the work finished during it.
- Due dates on the invoice that differ from the terms in the engagement letter.
How this works in Billed
Recurring Invoices
Billed's invoice software page says: "For clients you bill on a schedule, set up a recurring profile once." and "Billed creates the invoices automatically and either sends them or saves them as drafts for you to check."
Hourly Rate Projects
Billed's time tracking page says: "From the project dashboard you can invoice one task or several at once."
Invoice Reports
Billed's invoice software page says: "Invoice reports show which invoices are paid, partially paid or past due, and you can see who owes you money and send them a payment reminder."
Record Offline Payments
Billed's invoice software page says: "When a client pays by check or cash, record it as an offline payment so all your income is in one place."
Frequently asked questions
Start Invoicing With Billed
Set up your account and send your first invoice with Billed.
At a glance
| Invoice part | What an accountant puts there |
|---|---|
| Line items | One per service: retainer, fixed-fee return, hourly advisory |
| Period | The month or quarter each line covers |
| Hourly lines | Date, topic, hours and rate for each session |
| Notes | The engagement letter's date or reference |
| Due date | The payment terms in the engagement letter |
When this isn't for you
If a firm employs you and bills its clients itself, you won't send invoices of your own. This guide is for accountants who bill their clients directly.