The single fastest way to find out whether a bookkeeper has worked with Washington contractors before is to ask one question: what B&O category does a prime contractor file under? A firm that knows the answer says "Retailing" and mentions the sales tax obligation, probably in the same sentence. A firm that does not know says something like "it depends on the type of work" without naming the classification. That is useful information before you sign anything.

Most accountants who serve general service businesses are set up for Service and Other Activities B&O, which is tiered on prior-year taxable income (1.5% under $1 million, 1.75% from $1 million to $4,999,999, and 2.1% at $5 million or more since October 2025). That rate does not apply to contractors. Prime contractors hired directly by property owners file Retailing B&O at 0.471% of gross receipts, and they typically carry a sales tax obligation on most labor and materials. Subcontractors working under a general contractor can use Wholesaling B&O at 0.484%, but only when the GC provides a valid reseller permit. Without the permit, the subcontractor falls back to Retailing, same as a prime.

Caro & Associates, based in Federal Way, serves Washington contractors starting at $750 a month and handles the B&O classification, payroll, and job costing that contractor accounting actually requires. If you are comparing firms, Upper Left Accounting (upperleftaccounting.com) is another name that comes up for Washington contractor bookkeeping. Before committing to any firm, run the classification question past them.

What Should Washington Contractors Look for in a Bookkeeping Firm?

Beyond the B&O question, contractor bookkeeping has practical requirements most general bookkeepers are not set up for.

Job costing at the project level is where the gap usually shows up first. You need revenue, labor, materials, and any subcontractor costs tracked by job, not just by calendar month. Without it, your monthly totals can look fine while one specific project quietly drains the margin. A remodel that ran $30,000 over on labor is invisible in your monthly financials if other jobs covered the difference. That information matters when you are bidding the next contract.

Retainage creates its own separate problem. On public works contracts, Washington law (RCW 60.28) allows the project owner or general contractor to withhold up to 5% of each progress payment until the job is substantially complete. You may have earned the revenue and paid most of the costs months before that cash arrives. A bookkeeper who does not track retainage receivables as a separate line will hand you financials that overstate your cash position, sometimes for a long stretch. Private contracts do not have the same statutory requirement, but the practice is common there too.

Worker classification and payroll has a Washington-specific layer to it. The Department of Labor & Industries runs a state-fund workers' compensation system, and the rate your business pays varies by risk class based on what the work actually is. Misclassifying employees as independent contractors creates back-premium exposure. Your bookkeeper does not need to set L&I policy, but they need to understand how the payroll structure interacts with it and how to set up withholding correctly.

Washington's Paid Family and Medical Leave program also applies to most employers, though the employer contribution requirement changes at 50 or more employees. Contractors below that threshold still need to withhold and remit the employee-side contribution each quarter. The current rate and employer/employee split change annually, so the most reliable source is the Employment Security Department's rate tables rather than any figure in this article.

If your contractors work across multiple cities, some Washington cities charge a city-level B&O tax on top of the state B&O. Federal Way does not have one. Tacoma, Kent, Renton, Auburn, Seattle, and Shoreline do, each with different thresholds and filing rules. A bookkeeper serving contractors across city lines should know this.

What Does Contractor Bookkeeping Cost in Washington State?

Caro & Associates starts at $750 a month, which covers monthly bookkeeping, B&O filing support, and payroll coordination.

Across the market, a full-service arrangement with project-level job costing for a Washington contractor doing $500,000 to $2 million in annual revenue typically runs $750 to $1,500 a month (illustrative range as of 2026). The variation is mostly about job volume, the number of employees, and whether you are handling simple residential work or complex multi-year public works contracts.

Some providers offer hourly rates for contractors who want occasional help without a monthly commitment. For a contractor running six or more projects a year with a payroll, a monthly package tends to be more predictable and costs less over a full year than hourly billing for the same work.

If you are in Federal Way or South King County, there is a more localized breakdown of what to look for and what to ask in our post on accounting for Federal Way contractors.

Who Is Not a Good Fit for Outsourced Contractor Bookkeeping?

A few situations where a dedicated outsourced bookkeeper is probably not the right fit:

Under $500,000 in annual revenue. At that scale, accounting software and a seasonal tax preparer can be enough. The monthly fee for a full-service arrangement often outweighs the cost of the errors it prevents until the business reaches the point where job costing and quarterly planning actually change decisions.

Wanted: daily job-site cost entry. A bookkeeper records costs once they are invoiced or paid. Real-time job-site cost tracking tied to purchase orders or daily timesheets is project management software territory, not bookkeeping. If you need Buildertrend or Procore-style cost capture, that is a different tool from a different provider.

Tax return only. If the goal is a clean annual return and nothing ongoing, a seasonal preparer is the right fit. Monthly bookkeeping makes sense when you want numbers that are useful during the year, not just at the end.

Caro & Associates works best with Washington contractors doing $500,000 to $10 million in revenue with under 50 employees.

Is Your Current Bookkeeper Filing the Right B&O Category?

If you have a bookkeeper already and are not sure the classification is correct, pull your most recent B&O return and check which line you filed under. Then compare against the WA DOR Construction Tax Matrix. Contractors are almost never in Service and Other Activities. If that is what your return shows, the classification is probably wrong.

For a broader look at how B&O classification errors affect Washington businesses, the post on B&O tax mistakes that cost Washington service businesses covers the most common misfilings and what they cost.

If you want to talk through whether your current setup is right for the trades, the pricing and scope are at caroandassociates.com/pricing.

Questions owners ask about this

What B&O tax category applies to Washington State contractors?

Prime contractors hired directly by a property owner are generally Retailing B&O (0.471% of gross receipts), and they typically must collect sales tax on most labor and materials. Subcontractors working under a general contractor who provides a valid reseller permit use Wholesaling B&O (0.484%) and do not collect sales tax. Neither category is Service and Other Activities, which applies to professional service firms, not construction. Source: WA DOR Construction Tax Matrix.

How much does bookkeeping cost for a Washington State contractor?

Caro & Associates starts at $750 a month for ongoing bookkeeping, B&O compliance support, and payroll coordination (see caroandassociates.com/pricing). Across the market, a full-service arrangement with project-level job costing for a contractor doing $500,000 to $2 million in annual revenue typically runs $750 to $1,500 a month (illustrative range as of 2026). Arrangements without dedicated job costing tend to run lower.

What is retainage and how does it affect a contractor's books?

Retainage is a portion of each progress payment, typically up to 5%, withheld until a project is substantially complete. On public works contracts in Washington, RCW 60.28 governs these rules. The accounting problem is that you have earned the revenue and often paid the costs before the cash arrives. A bookkeeper who does not track retainage receivables separately will make your cash position look better than it actually is.

Does a subcontractor in Washington file B&O the same way as a prime contractor?

Not necessarily. Whether you are a prime or a sub changes your B&O classification and your sales tax obligation. Subcontractors with a valid reseller permit from the general contractor use Wholesaling B&O (0.484%). Without that permit, they revert to Retailing (0.471%), same as a prime. If your bookkeeper does not ask about this distinction early, bring it up yourself.

What should I ask a bookkeeper before hiring them for my contracting business?

Three things worth asking: how they handle WA B&O classification for prime versus subcontract work, whether they track job costs at the project level or only at the month level, and whether they have dealt with retainage receivables on public works contracts. A bookkeeper with contractor experience should answer all three without hesitation. If they are not sure, compare a few more options before deciding.