Accounting for Small Construction Business: Job Costs

Quick Answer: Accounting for a small construction business is ordinary bookkeeping plus one extra layer: every cost and every invoice is tied to a job. That lets you see profit job by job, bill in stages with retainage held back, track what you owe subcontractors and must report on Form 1099-NEC, and spot jobs that are over budget while there is still time to act.

A general contractor, remodeler or trade sub can show a profit for the year and still lose money on half its jobs. The books only reveal that if costs are recorded against the job that caused them. The rest of construction bookkeeping, from retainage to work in progress, grows out of that one habit.

What makes construction bookkeeping different?

Most small businesses sell something today and get paid soon after. Construction work stretches over weeks or months, is billed in pieces, and is paid with a portion held back until the end. Four consequences follow:

1. Profit is measured per job, not just per month. A busy month can contain the deposit for a big job and the final costs of an old one.
2. Revenue and cost timing drift apart. You may bill 40% of a contract while having spent 55% of the budget, or the reverse.
3. A lot of money sits with other people. Customers hold your retainage; you may hold your subs'.
4. Subcontractors are a major cost with their own paperwork: W-9s, certificates of insurance, lien waivers and year-end 1099s.

Job costing: the core habit

Give every job a number and every cost a code. A short cost code list beats a long one nobody follows:

Overhead that cannot be traced to one job (office rent, the owner's truck, accounting software) stays in normal expense accounts. Your chart of accounts handles those; job costing is a tag on top, usually a "job" or "class" field in accounting software or a column in a spreadsheet.

For each job, compare actual cost by code with the estimate you bid. The detailed spreadsheet version, with committed costs and change orders, is in the construction cost tracking spreadsheet guide.

Tying bank and card statements to jobs

Supply house charges on a card, rentals paid by transfer, subs paid by check: nearly every job cost passes through a bank or card statement. Each month, get the statements into rows (a CSV export, or QuickBankConvert for PDF statements) and add a Job column beside each line. Write the job number on receipts and in check memos as you go, and coding the statement takes minutes instead of an afternoon of guessing which lumber run went where. Lines that are left without a job at month end are either overhead or a mistake; both are worth knowing.

How do progress billing and retainage work?

On larger jobs you bill as work is completed instead of at the end, often against a schedule of values that splits the contract into line items. The customer pays each invoice less retainage, a percentage held back until completion, set by the contract.

Worked example: a $120,000 contract with 10% retainage.

1. First invoice: 25% complete, $30,000 earned. Retainage held: $3,000. Customer pays $27,000.
2. Second invoice: 60% complete, cumulative $72,000 earned, $42,000 this period. Retainage held: $4,200. Customer pays $37,800.
3. Final invoice: 100% complete, $48,000 this period, retainage $4,800. Customer pays $43,200.
4. After completion and final paperwork, the customer releases the $12,000 of retainage.

In the books, record each invoice at the full amount earned and track retainage receivable as its own balance per job. If you only record what the customer pays, $12,000 of revenue goes missing until the release, and your receivables understate what you are owed. The same logic applies in reverse when you hold retainage from your subs: it is a liability until you release it.

Subcontractors, W-9s and Form 1099-NEC

Before paying a new sub, collect a Form W-9 (name, taxpayer ID, entity type), a current certificate of insurance, and, where your state uses them, lien waivers with each payment.

At year end, payments for services to subs who are not corporations generally go on Form 1099-NEC (the instructions list the few kinds of payments to corporations that must still be reported). The threshold changed recently, so check the year:

• IRS Publication 334 (2025 edition) says to file Form 1099-NEC for each person you paid at least $600 during the year for services by a non-employee, including parts and materials.
• The current Instructions for Forms 1099-MISC and 1099-NEC say that for tax years beginning after 2025 the minimum threshold rose to $2,000, and may be adjusted for inflation starting in 2027. Both the IRS filing and the copy to the recipient are due by January 31.

Keep a running total per sub through the year: a PivotTable of your coded statement lines with Payee in rows, filtered to the subcontractor code, is enough. The IRS page on forms for independent contractors summarizes the paperwork. Whether a given worker is a contractor or an employee is a legal test, not a bookkeeping choice; ask a professional if in doubt.

Equipment

Tools and machines are assets, not just expenses. Publication 334 describes a de minimis safe harbor that lets you deduct amounts paid for tangible property up to $2,500 per item or invoice if you do not have an applicable financial statement ($5,000 if you do), when you treat them the same way in your books. Larger purchases are generally depreciated. Keep a simple equipment register: item, date bought, cost, serial number, and how it was paid. If you charge equipment time to jobs at an internal hourly rate, record that as a job cost with a matching credit to an equipment recovery account, so the overhead is spread across the jobs that use it.

Work in progress basics

At month or year end, some jobs are half done. A work-in-progress schedule compares, job by job, what you have billed with what you have earned based on percent complete. Billed more than earned means you are overbilled (cash ahead of work, a liability); billed less means underbilled (work ahead of cash, an asset). Even small contractors benefit from a quarterly WIP review, because a job that is steadily underbilled is often one that is over budget.

For taxes, some construction contracts fall under special long-term contract accounting. IRS Publication 538 does not cover those methods and points to section 460 of the Internal Revenue Code. Which method applies depends on your contracts and size, and is a question for a tax professional who works with contractors.

A monthly bookkeeping routine for a small contractor

• Code each bank and card line to a job or overhead; chase uncoded lines.
• Enter payroll hours by job.
• Send progress invoices and record retainage receivable.
• Pay subs, collect lien waivers, update each sub's year-to-date total.
• Reconcile each bank and card account to its statement.
• Update the job cost report and the WIP schedule; flag jobs over budget.

The general monthly bookkeeping cycle in bookkeeping for small business still applies underneath all of this; job costing is the layer that makes it useful for a builder.