What are the most common bookkeeping mistakes construction companies make?
A few mistakes show up again and again across contractors of every size. They usually start small and compound over time until the books don’t tell the owner what’s actually happening in the business.
Mixing personal and business expenses. This is the most common mistake and the hardest to untangle later. Running a material purchase through a personal card or paying the mortgage from the business account creates a mess that takes hours to sort out at tax time and can cost real money in missed deductions. Use one business bank account and one business credit card for everything related to the business, period.
Not separating job costs from overhead. Every expense needs to be coded as either a direct job cost or general overhead. Materials for the Rodriguez kitchen remodel are a job cost. The monthly software subscription is overhead. When everything gets lumped together, you can’t tell which projects made money and which ones lost it. Job costing only works if expenses get tagged to jobs as they happen, not reconstructed from memory months later.
Failing to track retainage separately. Retainage held back on a contract isn’t regular accounts receivable. It’s money you’ve earned but won’t collect until the job is complete and the owner signs off. Booking it alongside standard AR inflates your aging reports and hides how much cash is actually available to the business. Retainage belongs in its own account so you can see what’s outstanding and when it’s expected to release.
Not reconciling subcontractor payments to 1099s at year-end. Most contractors wait until January to pull 1099 amounts, then scramble when their records don’t match what they actually paid. Missing a sub on a 1099 creates IRS problems. Overstating creates a fight with the sub. Reconciling sub payments monthly makes year-end a confirmation step instead of a fire drill.
Not monitoring work-in-progress against budget. WIP reporting tells you whether projects are tracking to budget or running over. Contractors who only look at job costs after the project closes find out too late when they’ve already blown the number. A monthly WIP schedule comparing actual costs to budget by phase gives you time to adjust while the job is still active. This is the single most valuable report in construction accounting and most contractors don’t run it.
Other recurring issues include misclassifying employees as 1099 contractors, not accruing for materials received but not yet invoiced, and recording customer deposits as revenue before the work is performed. Each one distorts the financials in ways that make real decisions harder.
Most of these problems trace back to a bookkeeping setup that wasn’t built for construction in the first place. Generic QuickBooks files don’t track retainage, don’t separate job costs cleanly, and don’t produce WIP reports. Construction bookkeeping requires specific configuration that most contractors don’t have time to learn while they’re running jobs.
If the books feel unreliable or you can’t tell which projects are actually profitable, it’s usually a sign the underlying system needs work. The Pasadena bookkeepers at A Squared bring direct construction and real estate development accounting experience to the problem, so the fixes address what construction companies actually need to see.
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