Construction Bookkeeping: Job Costing, WIP and Retainage Explained

Construction is the industry where ordinary bookkeeping fails most obviously. A contractor can be profitable on paper and unable to make payroll, or look like they had a spectacular quarter because a large job was billed early. Neither is a reporting glitch. It is what happens when you run a project business on books designed for a shop.

Why construction books are different

Three structural things break the normal model.

Revenue does not arrive when you invoice. A job that runs eight months earns revenue across all eight, but gets billed on a schedule negotiated with the owner. Those two curves rarely match.

Part of your money is held back on purpose. Retainage — usually 5 to 10% of each payment — is withheld until the job is complete and accepted. You earned it, you have to fund the work, and you will not see it for months.

Costs belong to jobs, not to the month. Knowing you spent $180,000 on labour in July tells you nothing useful. Knowing you spent $46,000 of a budgeted $38,000 on the framing phase of one job tells you everything.

Job costing

Job costing means every dollar of cost is tagged to a job, and usually to a phase or cost code within it. Labour, materials, subcontractors, equipment, and an allocation of overhead.

Done properly, you can see mid-job that a phase is running over budget while there is still time to do something. Done poorly — costs booked to general categories and split up later, if at all — you find out a job lost money when it is finished and the crew has moved on.

This is the single highest-value thing a construction bookkeeper does, and it is the thing generalist bookkeepers most often skip, because it requires setting up the job and its budget before the work starts.

The WIP schedule

Work in progress is where the first two problems get reconciled. For every open job, the WIP schedule lists the contract value, costs incurred to date, the estimated total cost, the percentage complete, revenue earned, and revenue billed.

The last comparison is the important one:

• Costs in excess of billings (underbilling): you have earned more than you have invoiced. You are financing the owner's project out of your own cash.
• Billings in excess of costs (overbilling): you have invoiced more than you have earned. That cash is not profit; it is work you still owe.

Chronic underbilling is one of the most reliable early signals of a contractor heading for a cash crisis, and it is invisible on a normal profit and loss statement.

The WIP schedule is also the document your surety underwriter reads. Bonding capacity — the size of job you are allowed to bid — is set largely off WIP and working capital. For a contractor who bids bonded work, the quality of the WIP schedule directly limits the size of business they can win.

Percentage of completion

Most contractors of any size recognise revenue by percentage of completion: costs incurred divided by estimated total costs, applied to the contract value.

The estimate is the weak point. If the estimated total cost is optimistic, the job looks further along than it is and revenue gets pulled forward. Correcting the estimate later produces a sudden, ugly swing. Good construction accounting practice is to revisit cost estimates every month, not at the end.

Very small contractors on short jobs can often use completed contract or cash methods instead. Which method you may use for tax depends on your revenue and contract length, and it is worth asking a CPA rather than assuming.

What the market looks like

We profile 567 US accounting firms that name construction and trades as an industry they serve:

• 331 offer bookkeeping
• 272 offer tax preparation
• 164 offer audit and assurance
• 161 offer tax planning
• 136 offer payroll — relevant, because construction payroll carries certified payroll reporting and prevailing wage rules on public work
• 109 state they work remotely
• 99 name QuickBooks

Only 17 name Xero. If you run Xero and want a construction specialist, the pool is genuinely small; QuickBooks plus a construction add-on is the far more common stack in this industry.

What it costs

• Monthly bookkeeping with job costing: commonly $500 to $1,500 a month, above general bookkeeping because the cost coding is more work.
• WIP schedule preparation: often bundled into monthly work; standalone quarterly preparation runs a few hundred dollars a quarter.
• Reviewed or audited statements for bonding: $8,000 to $25,000 a year. Most sureties want reviewed statements at minimum above a certain bonding level.
• Certified payroll reporting: usually priced per job or per report on top of standard payroll.

Questions to ask a firm

1. Do you produce a WIP schedule monthly, and will you walk me through it?
2. How do you set up cost codes — do you use my existing structure or impose one?
3. Have your statements been accepted by a surety before, and by whom?
4. Do you handle certified payroll and prevailing wage reporting?
5. How do you allocate equipment and overhead to jobs?

If a firm cannot answer the first question crisply, they are doing general bookkeeping for a construction company, which is not the same thing.

Compare firms serving construction: construction bookkeeping, construction payroll, construction tax planning, or construction financial statements.

Figures from the AccountingNearYou dataset, 13 August 2026. Tax method eligibility and prevailing wage rules change; confirm current requirements with a CPA before relying on them.