Bookkeeping for Private Investigators: Retainers, Job Costing, and 1099 Compliance

A cheating-spouse case walks in the door with a $2,500 retainer. Over the next three weeks, the investigator burns 18 hours of surveillance, drives 340 miles, rents a long-lens camera for two nights, and pays a subcontractor $400 to cover a shift in another city. If the agency's books can't answer "did we make money on this case, and how much of that retainer is actually earned," the owner is flying blind — and private investigation is a business where blind spots compound fast.

Running a PI agency means juggling state licensing rules, client funds that aren't fully yours until you've earned them, subcontracted investigators whose worker classification can trigger real liability, and cases that run for weeks before you know whether they were profitable. None of that shows up in a generic small-business chart of accounts. Here's how to build books that actually match how investigation work happens.

Why Generic Bookkeeping Breaks Down for PI Firms​

Most small-business accounting software assumes you invoice for a product or a flat service and get paid. Investigation work doesn't fit that shape:

• You collect money before you've earned it. Retainers are prepaid against future hours and expenses, not revenue the day they hit your account.
• Every case has its own cost structure. Mileage, equipment rental, database and skip-trace fees, and subcontractor pay all attach to a specific case file — not to "the business" generally.
• Licensing is existential, not optional. An unlicensed or improperly bonded investigator's testimony and evidence can be challenged in court, and operating without a required license can be a criminal offense in some states.
• A meaningful share of your labor may be 1099 contractors covering surveillance shifts, out-of-territory work, or specialty skills (digital forensics, process serving) — and misclassifying them is one of the most common — and expensive — mistakes in the industry.

Get these four right and the rest of the books (payroll, taxes, overhead) look like any other service business.

Client Retainers: Track Them as a Liability, Not Revenue​

The single biggest bookkeeping mistake in this industry is booking a retainer as income the moment it arrives. It isn't income yet — it's client money you're holding against future work.

How to structure it:

1. Deposit retainers into a dedicated account, separate from your operating funds. Some states don't mandate a formal trust account for investigators the way bar associations do for attorneys, but treating retainers as client funds — not your money — is both good practice and a strong defense if a client ever disputes billing.
2. Book the retainer as a liability (Liabilities:ClientRetainers:ClientName) when received, not as revenue.
3. As you log billable hours and reimbursable expenses against the case, move the earned amount from the liability account to revenue. A weekly or milestone-based "retainer draw-down" invoice to the client keeps this current and gives them visibility into how their money is being spent.
4. Refund or apply the unearned balance when the case closes. If you bill hourly against a security retainer, whatever's left when the investigation ends belongs to the client, not you.

This structure — money in as a liability, earned in stages, unearned balance returned — is the same logic law firms use for trust accounting, and it holds up the same way if a client, a licensing board, or a court ever asks you to show your work.

Licensing and Bonding: Treat Compliance Costs as Fixed Overhead​

Most states require both the individual investigator and the agency to be licensed, and licensing regimes vary sharply — some states require thousands of hours of qualifying experience and a written exam, others require little more than a background check, and a few have no state-level licensing at all. On top of licensing, the majority of states that regulate PIs also require a surety bond, commonly in the $5,000–$25,000 range, which protects clients if the investigator's negligent or wrongful conduct causes financial harm.

Bookkeeping implications:

• Set up a recurring Expenses:Compliance:Licensing and Expenses:Compliance:SuretyBond line so renewal costs don't get miscoded as generic "insurance" or "fees" and disappear into noise.
• If you operate in multiple states — common once an agency starts fielding subcontractors elsewhere — track licensing and bond costs per state, since renewal dates, CE requirements, and bond amounts won't line up.
• Keep license and bond expiration dates next to your books, not just in a filing cabinet. A lapsed license doesn't just risk a fine — evidence gathered by an unlicensed investigator can be thrown out, which is a business-ending problem for a case-based firm.

Per-Case Job Costing: The Only Way to Know What You're Actually Earning​

An hourly rate that looks profitable on paper can evaporate once mileage, equipment, database fees, and subcontractor pay are netted out. Surveillance work in particular carries real direct costs — most agencies charge separately for mileage on top of the hourly rate, and multi-day surveillance can mean $800–$1,200 per day in labor before a single expense is added.

Set up job costing at the case level:

• Create a class or tag per case (most accounting tools support this) so every hour, mileage entry, equipment rental, and third-party fee rolls up to one case-level profitability number.
• Track direct case costs separately from overhead: mileage, equipment rental or depreciation, database/skip-trace subscription fees, subcontractor pay, and court-related costs (filing, service of process) all belong to the case, not general operating expenses.
• Calculate realized revenue per case — actual amount billed and collected divided by the case's total loaded cost (labor + direct expenses) — the same "realization rate" concept professional services firms use to catch scope creep and underbilling before it erodes margin across a whole year of cases.
• Review closed cases monthly, not just annually. A pattern of low-realization cases in one category (say, low-dollar background checks accepted to fill slow weeks) is a pricing problem you want to catch in Q2, not in your tax return.

Mileage and Equipment: Don't Leave Deductions on the Table​

Surveillance work generates unusually heavy vehicle use, and the IRS standard mileage rate makes tracking it worth real money — every mile logged is deductible business use, separate from the mileage you may already be billing clients for.

• Log mileage by case, not just in aggregate. This does double duty: it supports your tax deduction and it's the same data you need for accurate per-case job costing above.
• Camera equipment, GPS trackers, audio/video recording gear, and covert equipment are typically deductible as business equipment — either expensed under Section 179 in the year purchased or depreciated, depending on cost and your tax situation.
• A dedicated home office used exclusively for report writing, case management, and client calls can qualify for the home office deduction — but "exclusively" is doing real work in that sentence; a shared family space won't hold up.
• Keep equipment purchases in their own expense category, separate from consumables (batteries, storage media, data plans), so you can see replacement cycles coming instead of getting surprised by a $3,000 lens purchase in December.

Subcontractor Classification: Get 1099 vs. Employee Right​

Agencies commonly bring in other licensed investigators for coverage — a surveillance shift in another city, a specialty skill, or overflow during a busy stretch — and pay them as 1099 subcontractors. The IRS doesn't care what you call the arrangement or which form you file; classification turns on behavioral control, financial control, and the relationship of the parties.

Signs a worker is a legitimate subcontractor:

• They use their own vehicle, equipment, and licensing, and can decline assignments.
• They control how the surveillance or investigation is conducted, not just when.
• They work for other agencies or clients, not exclusively for you.
• They invoice you and bear some financial risk (no guaranteed pay regardless of outcome).

Signs point toward employee, even if you're issuing a 1099:

• You set their schedule and dictate methods step by step.
• You provide their equipment and vehicle.
• They work exclusively for your agency on an ongoing basis.

Misclassification exposure is real: back payroll taxes, penalties, and — in states with strict tests like California's ABC standard — potential unemployment and workers' comp claims. Note that some states carve out licensed private investigators as a recognized profession in independent-contractor rules, but that carve-out isn't automatic protection; the underlying facts of the working relationship still matter. Bookkeeping fix: keep signed subcontractor agreements, W-9s, and proof of their own licensing on file, and route 1099 pay through a distinct Expenses:Subcontractors account (tagged by case) so you can see at year-end exactly who was paid what, and back it up with documentation if a state agency ever asks.

The KPIs Worth Watching Monthly​

Once retainers are tracked as liabilities and cases are costed individually, three numbers tell you most of what you need to know about the health of the agency:

1. Realization rate — billed and collected revenue divided by the full loaded cost of the work. Falling below roughly 85–90% consistently signals underpricing, scope creep, or write-offs you're absorbing without noticing.
2. Case profitability distribution — not just the average, but how many cases lose money once direct costs are netted out. A single unprofitable case category can quietly subsidize the rest of your book.
3. Recovered-expense ratio — the share of billable mileage, equipment, and third-party fees you actually invoice and collect versus what you spend. Agencies that eat expenses "to keep the client happy" too often are giving away margin case by case.

Keep Your Case Books as Clean as Your Case Files​

Investigation work runs on documentation — chain of custody, timestamps, verifiable records. Your books deserve the same rigor. Beancount.io provides plain-text accounting that gives you complete transparency and an auditable trail for every retainer, case cost, and subcontractor payment — no black-box software, no vendor lock-in. Get started for free and see why service businesses that live and die by their records are switching to plain-text accounting.