Bookkeeping for Professional-Service Firms: What's Different and Where It Goes Wrong

A professional-service firm sells time and expertise, and that changes what its books have to track. Money often arrives before the work is done. Work is often done before it is billed. Some of what the firm spends belongs on a client's invoice, and a law practice holds money that is not its own at all. A standard setup handles none of this on its own.

This guide covers what is different about bookkeeping for professional services, one area at a time: retainers, unbilled work, costs paid on a client's behalf, profit by client or project, and trust accounts. For each, it explains how the books should handle it and where it usually goes wrong. It is written for law practices, agencies, consultancies, and design & engineering firms: firms that bill for their work by the hour, the project or the month.

What makes bookkeeping for professional-service firms different?

Timing and ownership. When a business sells a product, the sale and the income usually happen together. In a professional-service firm, the money, the work and the bill often land in different months, and some of the money passing through belongs to clients. The books have to show which is which.

Five areas need handling that a generic setup does not provide for:

Area	How the books should handle it	Where it goes wrong
Retainers and advance payments	Held as a liability until the work is done, then moved to income	Booked as income the day the money arrives
Unbilled work	Tracked by client and project until it is invoiced	Invisible until it is invoiced, and written off if it sits unbilled too long
Costs paid for clients	Marked billable to the client when entered, then added to an invoice	Recorded as an ordinary expense and never billed
Profit by client or project	Income and costs assigned to each project, engagement or matter	One income account, so only the firm's total shows
Client trust accounts	Reconciled three ways, with a ledger for each client	Checked against the bank only, so errors in client ledgers go unseen

The sections below take each area in turn.

How should a retainer be recorded in the books?

As a liability, until the work it pays for is done. A retainer paid in advance is money the firm is holding for future work, not money it has earned. A bookkeeping firm's guide to retainer fees, published in September 2024, says to record unearned retainers as liabilities until the services are performed, and then move them to income.

The same guide separates two kinds. A general retainer secures the firm's availability over a period and does not pay for any specific work. A retainer paid for a defined project is earned as that work is finished. The engagement letter should say which kind it is, and whether any unused part can be refunded.

In QuickBooks® Online, that means an account on the balance sheet for client prepayments. One software company's help page on recording retainers in QuickBooks Online sets it up as an Other Current Liabilities account with the detail type Deferred Revenue, so the balance sheet shows what clients have paid ahead. As invoices are issued, the prepayment is applied against them, and the liability falls as the income is recognized.

A hypothetical retainer, booked two ways

Take a hypothetical agency paid $9,000 in January for a three-month project. Booked as income when it arrives, January looks like a record month, and February and March look like losses, though the work was steady all quarter. Booked as a liability and moved to income as the work is done, each month shows the $3,000 it earned, and the balance sheet shows the work the firm still owes.

The error is common because the deposit lands in the bank like any other payment. If the bank feed codes it to income, nobody notices until the months stop making sense. A law practice has a further rule to follow. Another bookkeeping firm's guide, on trust accounts and reviewed in July 2026, says unearned retainers belong in the trust account, and that depositing them anywhere else is commingling.

A retainer is money you are holding for the client, not money you have earned yet.
Christopher Wilson, Cilson Bookkeeping

Why does unbilled work go missing from a service firm's books?

Because most books record income only when an invoice goes out, or when the payment comes in. Work that is done but not yet invoiced sits outside both. A practice management software company, in an article dated October 2026, describes this work in progress as the value of time and costs spent on a job but not yet invoiced to the client.

On books kept on the cash basis, income shows up when the money arrives, so a month of hard work can show almost nothing. On the accrual basis, income shows up when the invoice is issued. Neither shows the hours sitting in a timesheet that nobody has billed.

The same article lists what goes wrong when nobody tracks it. Time that is never recorded never becomes work in progress at all. When invoices go out only at the end of a project, the unbilled amount stays hidden until billing starts. Cash flow gets harder to forecast, and work in progress that ages long enough ends up written off, by decision or by default.

The fix starts outside the ledger. Time has to be recorded against the client and the project as the work happens, and someone has to review what is unbilled before each round of invoices. The books then pick it up as it is billed.

How should costs paid for clients be handled in bookkeeping?

Each one should be marked as billable to the client when it is entered, so it reaches that client's next invoice. Think of filing fees, travel or printing paid on a client's behalf. A cost the firm pays and never bills comes straight out of its profit.

QuickBooks Online has a feature for this. Intuit's help article on entering billable expenses, updated in August 2026, explains how it works:

Turn it on. Billable expense tracking is switched on in the expense settings, where a default markup rate can also be set.
Mark the cost. When a bill, expense or check is entered, the Billable box is ticked and the customer is chosen.
Bill it. When an invoice is created for that customer, an Add to invoice window lists the billable expenses, and each one can be added.

The article describes the feature in QuickBooks Online Plus and Advanced.

Where this goes wrong is usually the first step. A cost recorded as an ordinary expense, with no customer attached, never reaches an invoice. The same cost entered twice, once by hand and once from the bank feed, can be billed twice. And a cost attached to the wrong client turns up on the wrong invoice, which is a harder conversation than a missing charge.

How can a firm see profit by client or project in its books?

By assigning income and costs to each project, engagement or matter as they are recorded. A profit and loss with one income account shows the firm's total and nothing more. A good year can hide clients that lost money, and a client whose work keeps growing while the fee stays the same looks like a busy month rather than a problem.

Tracking it this way is called job costing, or project accounting. In QuickBooks Online it runs through Projects, which comes with the Plus and Advanced plans. Intuit's help article on invoicing project expenses, updated in August 2026, explains that once Projects is set up, expenses and timesheets marked billable can be invoiced to the customer, and QuickBooks links both the expense and the invoice to the project.

The structure matters as much as the feature. Someone has to decide how projects are named and which costs belong to a project rather than to overhead. Without that, each cost lands wherever the person entering it chose, and the margin figures cannot be trusted. Time matters too. For a firm whose main cost is its people, a project's margin is only as good as the time recorded against it.

How does trust accounting work in a law practice's books?

A law practice keeps money it holds for clients in a trust account, often a pooled account known as an IOLTA account, and that money is not the firm's. The books track it two ways: one balance for the account as a whole, and a separate ledger for each client showing what that client has on deposit.

The check that holds this together is the three-way reconciliation. A bookkeeping firm's guide to trust account reconciliation, reviewed in July 2026, names the three balances it compares:

the bank statement balance for the trust account;
the trust balance in the general ledger, which is what the books say;
the total of every client's ledger.

A legal software company's guide, updated in August 2026, adds that the bank balance is adjusted for deposits and withdrawals that have not cleared, and that all three must match.

Why three, and not the usual two? An ordinary bank reconciliation compares the bank with the books. In a trust account those two can agree while one client's money sits under the wrong matter. The trust account guide lists what only the third comparison catches: a deposit posted to the wrong client, a payment that overdrew a client's balance, and money left in trust for a matter that closed months ago.

On timing, that guide says most states expect the reconciliation monthly and a few allow quarterly. The rules differ from state to state, so the one that governs is your own state's. Mixing the firm's money with client money is called commingling, and the guide notes that commingling and recordkeeping errors can be sanctioned even when no client loses money. It calls bank fees charged to the trust account the most common problem, and suggests having the bank charge fees to the operating account instead.

Why a standard setup misses what professional-service firms need

Most of these problems start on day one. A new QuickBooks Online file comes with a standard list of accounts, and features such as billable expense tracking stay off until someone turns them on. Nothing in the file knows that the firm takes retainers, bills costs back or holds client money. So each of those gets handled the nearest way the default file allows, which is usually as ordinary income or ordinary expense.

A setup built for a professional-service firm settles these questions before the first transaction:

a liability account for retainers and other money clients pay ahead;
billable expense tracking turned on, so client costs are marked as they are entered;
income and cost accounts that keep project work apart from overhead, so job costing can be added later without a rebuild;
for a law practice, trust and operating accounts kept apart from the first entry, with client funds recorded as a liability rather than as income.

Putting these right after a year of transactions can mean going back through that whole year. Building them in at the start is far simpler.

How I handle these areas in a firm's books

For law practices, I do a three-way IOLTA reconciliation every month. For firms that use job costing, I code costs to each project, track the costs paid on a client's behalf so they get billed back, and deliver a margin figure per project with the monthly reports. Job costing is a one-time setup fee, and the ongoing coding is included in the monthly bookkeeping quote. It needs QuickBooks Online Plus or Advanced, and I check that before quoting.

Where the file itself does not fit the firm, my setup and migration service builds the chart of accounts around how the firm works. Monthly bookkeeping and job costing each have a page with the details.

A quick check of a professional-service firm's books

Retainers sit in a liability account until the work is done.
Unbilled work is reviewed before every round of invoices.
Client costs are marked billable when they are entered.
Margin can be read by client or project, not only for the whole firm.
For a law practice, the three trust balances agree every month.
No client ledger in the trust account shows a negative balance.

Professional-service firm bookkeeping, in short

A professional-service firm's books have to keep timing and ownership straight. Retainers are held as a liability until they are earned. Unbilled work is tracked until it is invoiced. Costs paid for clients are marked billable when they are entered. Income and costs are assigned by project, so the margin shows where it is made. And a law practice's trust account is reconciled three ways, so each client's balance is right as well as the total. Most of the trouble starts with a setup that was never told how the firm works. For the checks an owner can run on books someone else keeps, see how to spot errors in your books.