Which fixed-fee bookkeeping clients pay for their hours?

A fixed monthly fee looks the same every month. The hours behind it don't. A quarterly filing lands in one month. A client opens a second location and the receipts double. Small requests add up. By the end of the quarter, some clients have paid well for their hours and some haven't covered them.

This guide gives each client two figures and shows how to log the work so the figures are right. Then it works through a fictional quarter at a one-person practice, and covers what to do about a client that costs more than it pays.

Two figures per client

A client pays for its hours when its fees, divided by its hours, come to more than an hour of your time costs you. So each client gets two figures for the quarter:

Effective rate        = fees ÷ hours
Contribution          = fees − outside costs − hours × internal hourly cost
Contribution per hour = contribution ÷ hours

The effective rate is what the client actually paid for each hour of work. It needs no cost estimate. You can set it beside the hourly rate you charge for extra work, or what you'd quote a new client for the same job.

Contribution per hour is what each hour left after it was paid for. With no outside costs, it's the effective rate minus your internal hourly cost. Below zero, the client costs more to serve than it pays.

Contribution here means contribution before overhead: fees minus the cost of delivering the work, before rent, software and other running costs. Client profitability: contribution before overhead explains it with a worked month.

Your internal hourly cost is what an hour of delivery costs you, not what you charge. In a one-person practice, use what you'd pay someone else to do the work. How to set an internal hourly cost rate shows how to work one out, including for your own hours.

Outside costs are what you pay others for one client's work, such as a contract bookkeeper's invoice. Software you'd pay for with or without the client stays in overhead.

How to log it: one row per job

Step 1: Give each job its own row

Use one row per client, job and month. A fixed-fee book can have five kinds of job:

• Monthly bookkeeping: the monthly fee and its hours.
• Work included in the fee, such as quarterly returns: a fee of 0, with its hours.
• Work billed on top, such as a return you price separately: its own fee and hours.
• Catch-up work for a new client: its own fee, hours and outside costs, read apart from the monthly work.
• Out-of-scope work you didn't bill: a fee of 0, with its hours.

Keep each job's name the same every month, so the rows line up when you add them.

Step 2: Log quarterly work in the month you do it

Some work comes once a quarter. Employers who file Form 941, the federal return for withheld income tax, Social Security and Medicare, file it for each quarter. It's due by the last day of the month after the quarter ends, so the April to June return is due July 31. Employers the IRS has told to file Form 944 file once a year instead.

If the monthly fee includes that work, log its hours in the month you do them, at a fee of 0. That month will look thin. The quarter will be right.

Step 3: Log the unbilled extras too

A request outside the engagement still takes hours. Log it at a fee of 0 under its own job name. What scope creep and overservicing cost, per client shows how to tag that time as you go, and what the extra hours cost you.

Step 4: Add up the quarter, then divide

At quarter-end, total each client's fees, outside costs and hours across all its rows. Then work out the two figures. Add first and divide once. Averaging three monthly per-hour figures would let a light month count as much as a heavy one.

A worked example (fictional)

Fictional example. Tallowgate Bookkeeping is not a real business. The figures are illustrative and are not a customer result.

Tallowgate Bookkeeping is a one-person practice that bills small businesses a fixed monthly fee in US dollars. Its clients below are fictional too. The owner uses an internal cost of US$40 an hour: what it would cost to pay someone else for the work, spread over delivery hours. None of the three clients had outside costs this quarter.

Here is July, one row per job:

Client (fictional)	Job	Fee	Hours
Wrenhurst Physio	Monthly bookkeeping	US$650	7
Wrenhurst Physio	Quarterly payroll returns (in fee)	US$0	3
Callowbrook Cafe	Monthly bookkeeping	US$600	12
Brindlemoor Plumbing	Monthly bookkeeping	US$450	14.5
Brindlemoor Plumbing	Out of scope (unbilled)	US$0	4
Total		US$1,700	40.5

Two rows have a fee of US$0. Wrenhurst Physio's fee includes its quarterly payroll returns, and the April to June returns were done in July. Brindlemoor Plumbing's 4 hours went on a clean-up of supplier statements that nobody agreed in advance.

Each client, month by month:

Client (fictional)	Month	Fee	Hours	Contribution	Effective rate	Per hour
Wrenhurst Physio	July	US$650	10	US$250	US$65.00	US$25.00
Wrenhurst Physio	August	US$650	7.5	US$350	US$86.67	US$46.67
Wrenhurst Physio	September	US$650	7	US$370	US$92.86	US$52.86
Callowbrook Cafe	July	US$600	12	US$120	US$50.00	US$10.00
Callowbrook Cafe	August	US$600	12.5	US$100	US$48.00	US$8.00
Callowbrook Cafe	September	US$850	12	US$370	US$70.83	US$30.83
Brindlemoor Plumbing	July	US$450	18.5	−US$290	US$24.32	−US$15.68
Brindlemoor Plumbing	August	US$450	14	−US$110	US$32.14	−US$7.86
Brindlemoor Plumbing	September	US$450	18.5	−US$290	US$24.32	−US$15.68

The arithmetic for Wrenhurst Physio in July:

• Hours: 7 + 3 = 10.
• Contribution: US$650 − 10 × US$40 = US$250, or 38.5% of the fee.
• Effective rate: US$650 ÷ 10 = US$65.00 an hour.
• Contribution per hour: US$250 ÷ 10 = US$25.00, which is US$65.00 − US$40.

Brindlemoor's July and September rows each add a clean-up: 14.5 + 4 = 18.5 hours in July, and 15 + 3.5 = 18.5 in September. Callowbrook's fee rose to US$850 from September. More on both below.

Now the quarter, with each client's rows added first:

Client (fictional)	Fees	Hours	Cost at US$40	Contribution	Margin	Effective rate	Per hour
Wrenhurst Physio	US$1,950	24.5	US$980	US$970	49.7%	US$79.59	US$39.59
Callowbrook Cafe	US$2,050	36.5	US$1,460	US$590	28.8%	US$56.16	US$16.16
Brindlemoor Plumbing	US$1,350	51	US$2,040	−US$690	−51.1%	US$26.47	−US$13.53
Total	US$5,350	112	US$4,480	US$870	16.3%	US$47.77	US$7.77

For Wrenhurst Physio, the fees are 3 × US$650 = US$1,950 and the hours are 10 + 7.5 + 7 = 24.5. Contribution is US$1,950 − 24.5 × US$40 = US$970. The effective rate is US$1,950 ÷ 24.5 = US$79.59, and contribution per hour is US$970 ÷ 24.5 = US$39.59.

Across the practice, Wrenhurst and Callowbrook contributed US$970 + US$590 = US$1,560. Brindlemoor took US$690 of that back, which leaves US$870 for the quarter.

Read a quarter, not a month

Each client tells a different story, and no single month tells it.

Wrenhurst Physio: July is the filing month, not a bad month. July alone came to US$25.00 an hour, against US$46.67 in August and US$52.86 in September. The 3 hours of payroll returns come every quarter, and the fee has to carry them across all three months. Over the quarter, Wrenhurst left US$39.59 an hour. Judged on July, it looks weak. Judged on September, it looks better than it is.

Callowbrook Cafe: read the months since the change. Before its second location opened in June, the monthly work took 8 hours in April and 8.5 in May. At US$600, April left US$600 − 8 × US$40 = US$280, or US$35.00 an hour. May left US$600 − 8.5 × US$40 = US$260, or US$30.59 an hour. With two locations and the same fee, July and August left US$10.00 and US$8.00. Tallowgate repriced the client to US$850 from September, and September came to US$30.83, back near where the client started. The quarter's US$16.16 mixes two fees, so it describes neither. One month at the new fee is a start. Read October and November before you call it settled.

Brindlemoor Plumbing: below your cost every month. Its effective rate was US$26.47 an hour, and an hour costs Tallowgate US$40. It took 45.5% of the practice's hours (51 of 112) for 25.2% of its fees (US$1,350 of US$5,350). The unbilled clean-up isn't the whole story. The monthly work alone took 14.5 + 14 + 15 = 43.5 hours. At cost, that's 43.5 × US$40 = US$1,740, which is US$390 more than the quarter's fees.

Three habits keep these readings honest:

• Log the included work. Leave Wrenhurst's 3 hours out, and the client looks better than it is every quarter.
• Log the unbilled hours. They're where a client's cost hides.
• Give your own hours a cost. At zero, every client pays for its hours, and the figures stop meaning anything.

When a client is under your cost

Start with the lowest fee that covers the hours:

Break-even fee = average monthly hours × internal hourly cost
                 + average monthly outside costs

Break-even covers the hours and nothing else: no overhead, no profit. It's a floor, not a price.

For Brindlemoor Plumbing:

• All the work: 51 ÷ 3 = 17 hours a month, so 17 × US$40 = US$680.
• Monthly work only, if the clean-ups stopped: 43.5 ÷ 3 = 14.5 hours a month, so 14.5 × US$40 = US$580.

The fee is US$450, so it's US$130 a month short even with no clean-ups, and US$230 short with them. Stopping the extras won't fix this client on its own.

There are three moves:

• Reprice: a new fee for the work the client actually needs.
• Rescope: less work for the same fee, for example by agreeing what the client sends and when.
• Bill the extra: agree a rate for clean-up work, and quote it before you start.

Check your engagement letter for notice periods and price-review dates first. When to reprice, rescope or drop a client shows how to choose between the three, using a target per hour of your own. It also shows how to raise it with the client.

What this method doesn't do

• It sees only the hours you log. Quick emails and calls that never reach a timesheet make every client look better than it is.
• It rests on one internal cost per hour. If that estimate is off, every contribution figure moves with it. The effective rate doesn't, which is one reason to keep both.
• The break-even fee covers delivery hours only. It leaves out overhead, such as software, insurance and your own admin time, and any profit.
• It looks back at closed months. It doesn't forecast, and it can't tell you what a client will agree to pay.
• It doesn't decide what the fee covers. Your engagement letter does. If the wording is unclear, ask a lawyer before you bill for disputed work.
• It's management arithmetic for your practice, not your accounts or your tax position. Form 941 appears only to show why some work comes once a quarter. For your own tax and filing questions, or a client's, ask an accountant or other tax professional.

Where the tracker fits

The Client Profitability Tracker shows contribution before overhead, margin and contribution per delivery hour for each client, for the month you pick. Negative results stay visible. It takes one row per client project per month, so each job can be its own project: monthly bookkeeping, quarterly returns, out-of-scope work. A repeated client, project and month is flagged for review.

It has no column for the effective rate, scoped hours or transaction counts. Work out the effective rate beside it: fees divided by delivery hours. Its table by client covers one month at a time. For the quarter, switch the report month three times, or add each client's months by hand.

It's for your practice's own view of its clients. It keeps no client's books, and it does no invoicing or sales tax. Entry is manual, and the workbook is tested in Excel 365 desktop. Like this guide, it stops before overhead. The formulas above work in any spreadsheet.

Independence

Metricvalley is independent. This guide isn't affiliated with, or endorsed by, the Internal Revenue Service. Nothing in this guide is tax, payroll or legal advice.

Sources and method

Every figure in the worked example is fictional (Tallowgate Bookkeeping). Contribution and contribution per hour apply the contribution-margin idea, revenue minus the costs that move with the work, to each client's hours. The effective rate and the break-even fee are the arithmetic set out above. The Form 941 filing rules come from the IRS pages below.

• Internal Revenue Service, Instructions for Form 941 (03/2026) (revision dated March 2026), read Oct 12, 2026.
• Internal Revenue Service, About Form 941, Employer's Quarterly Federal Tax Return (page updated Jul 22, 2026), read Oct 12, 2026.
• OpenStax, 3.1 Explain Contribution Margin and Calculate Contribution Margin per Unit, Contribution Margin Ratio, and Total Contribution Margin (textbook: Principles of Accounting, Volume 2: Managerial Accounting), read Oct 12, 2026.