The biggest mistake contractors make is not tracking costs by job. They categorize expenses as “materials” or “labor” without assigning them to specific projects. At year end they know whether the company made money overall but have no idea which jobs were profitable. A kitchen remodel might have looked good on paper but actually lost money because framing labor ran over and no one caught it. Proper job costing for contractors takes discipline but pays off in knowing which work makes money and which drains the business.

Confusing deposits with revenue comes in second. A customer pays $10,000 upfront before work starts. That’s not income yet. It’s a liability until you actually perform the work. Recording deposits as revenue makes January look great and March look terrible when expenses pile up but the money was already counted. Progress billing creates similar confusion. You bill $25,000 against a phase that’s 80% complete but only $20,000 is actually earned. Contractors who don’t track earned versus billed can’t produce accurate financial statements for banks or bonding companies.

Not reconciling accounts regularly lets errors compound. A charge gets miscoded, a deposit gets missed, and by the time anyone notices it’s six months later. Weekly reconciliation catches mistakes while they’re easy to fix and the details are still fresh.

Mixing personal and business expenses happens constantly. Using the business card at the hardware store for a personal project, running personal gas through the company account, buying job materials on a personal card and never recording them. Tax time becomes a forensic exercise trying to separate deductible expenses from personal purchases.

Missing W-9s for subcontractors creates a scramble every January. Massachusetts requires 1099s for anyone you pay over $600 for services. If you don’t collect W-9s from subs when you hire them, you’re chasing paperwork at year end when they’re busy on other jobs and slow to respond.

Skipping monthly closes means you’re always working with outdated numbers. Financial statements from three months ago don’t help you price the next job or decide whether to take on more work. A structured close with reconciliation and review each month gives you information you can actually act on.

These mistakes add up. Contractors lose money on jobs without realizing it, overpay on taxes, and scramble every spring to reconstruct records. If you’re running a contracting business in the MetroWest or Greater Boston area, working with small business bookkeeping in MetroWest Massachusetts that understands construction workflows makes a real difference. The goal is clean books that show you what’s actually happening in your business.