How to Invoice as a Private Investigator
What goes on an investigator's invoice and what stays off it, with one worked example from the deposit to the final invoice.
In the US, the Bureau of Labor Statistics says (page last modified October 29, 2026): "Private detectives and investigators gather, analyze, and report information to clients regarding legal or personal matters." An invoice for this kind of work lists the hours and the expenses the client is paying for, without repeating case details on a document other people may handle.
This guide covers billing only. It doesn't give licensing or legal advice; for licensing, ask the agency in the state where you work. One example of a state source is California's Bureau of Security and Investigative Services fact sheet, linked below.
Worked example (sample figures, not suggested rates): an attorney asks for 20 hours of surveillance and records research at 85.00 an hour, plus a database search at 45.00, for 1,745.00. The invoice uses a payment schedule: 872.50 due before work starts and 872.50 due when the report is delivered. The case needs 4 more hours and 120 miles of driving at the 0.70 a mile set in the engagement letter, so a final invoice bills 4 × 85.00 = 340.00 plus 84.00, or 424.00. The case bills 1,745.00 + 424.00 = 2,169.00 in all.
Step-by-step invoicing guide
- 1
Put the terms in the engagement letter
Write the hourly rate, which expenses the client pays for, the mileage rate and the deposit before you start. Ask the client what reference they want on the invoice, such as a case or matter number.
- 2
Ask for a deposit up front
Billed's help center says "A payment schedule lets you add a payment plan to the invoices." It says to "Choose a suitable option among percentage or flat amount" and "Fill out the payment amount and due date of each payment." Set the first payment due before work starts and the rest due when you deliver the report.
- 3
Track your hours
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. From the project dashboard you can invoice one task or several at once."
- 4
Bill hours by date and activity type
On each time line, give the date, the hours and a general activity type, such as "Surveillance" or "Records research". Keep names, addresses and findings in your report, not on the invoice. Billed's help center says: "Click 'Add a Line Item' and fill this section to charge against new items and services."
- 5
Pass through the expenses the client pays
Record mileage, database fees and other costs your engagement letter says the client covers. Billed's help center says: "If there are any unbilled expenses of a particular client, you can add these expenses to the client's next invoice." It adds: "The expense will appear as a line item in the invoice."
- 6
Add the client's reference
Put the case or matter number in the notes, so the client's accounts payable staff can match the invoice. Billed's help center says: "You can add additional details related to the transaction in 'Additional Notes' while creating an invoice." It adds: "You can also add any terms and conditions in this section."
- 7
Add a due date and reminders
Billed's invoice software page says: "Set a due date on each invoice so your client knows when to pay." Billed's help center says: "Turn on the 'Payment Reminders' option while creating or editing an invoice." It adds: "You can set a schedule of payment reminders before and after the invoice's due date."
Tips for private investigator invoicing
- Use the client's own case or matter number, so nobody has to read case details to file the invoice.
- Keep each receipt with your case file, so you can show what an expense line was for if the client asks.
- If the case will need more hours than you estimated, warn the client before going over, and bill the extra hours on a final invoice.
- Send the final invoice with the report, while the client is reviewing your findings.
Common invoicing mistakes to avoid
- Writing subjects' names or locations in line descriptions.
- Starting work before the deposit is paid.
- Billing mileage or database fees the engagement letter doesn't mention.
- Going past the estimated hours without telling the client.
How this works in Billed
Deposit and balance
Set a deposit due before work starts and the balance due when you deliver the report, on one invoice (Billed's help center).
Hourly projects
Track time on a project with an hourly rate, and bill the tasks you select (Billed's time tracking page).
Expenses on the next invoice
Bill database fees and other costs you paid for a case on the next invoice you send that client (Billed's help center).
Ways to pay
Billed's invoice software page says: "Connect Stripe and each invoice gets a pay button for card payments, or connect PayPal to add a PayPal option." It also 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
| On the invoice | Keep off the invoice |
|---|---|
| Date, hours and activity type | Subjects' names and addresses |
| Mileage and fees the client pays for | Places visited |
| The client's case or matter number | Findings |
| Deposit and balance | Anything that belongs in the report |
When this isn't for you
This guide is for investigators who invoice their own clients. If an agency employs you, the agency bills the client. It doesn't give licensing or legal advice.