The basic formula is simple. Take your total annual overhead costs and divide by your total billable labor hours for the year. That gives you an overhead rate per labor hour. When you bid a job, multiply the rate by estimated labor hours to get the overhead amount to include.

First you need to know what counts as overhead. Add up everything you pay that isn’t directly tied to a specific job. Office rent, utilities, vehicle payments and fuel for non-job travel, insurance premiums, administrative wages, accounting and legal fees, software subscriptions, marketing costs, cell phones, licenses, bonding, and small tools and equipment. If you pay it whether or not you’re working a job, it’s overhead.

Next, estimate your billable hours for the year. Not total hours worked, but hours you can actually bill to jobs. If you run a crew of four and expect each person to log 1,800 billable hours, that’s 7,200 hours. Be realistic here because overestimating billable hours means your overhead rate comes out too low.

Now do the math. If your annual overhead runs $180,000 and you expect 6,000 billable hours, your overhead rate is $30 per labor hour. A project you estimate at 200 labor hours would carry $6,000 in overhead. Add that to your direct costs for labor, materials, and subs before adding your profit margin.

Some contractors prefer using direct labor cost as the base instead of hours. Divide total overhead by total annual labor cost and express the rate as a percentage. If overhead is $180,000 and annual labor cost is $300,000, your overhead rate is 60%. A job with $10,000 in labor costs would carry $6,000 in overhead. Either method works as long as you use it consistently.

Common mistakes include forgetting to count all overhead costs, using gross hours instead of billable hours, and failing to update the rate when things change. If you hire office help, lease a bigger shop, or add a truck, your overhead rate needs to reflect the new reality. Review the rate at least annually and compare your projected overhead to what you actually spent.

The overhead rate only covers your costs. It doesn’t include profit. After adding overhead to direct costs, you still need to mark up for profit. Construction businesses that stay busy but don’t make money often have overhead rates that are too low or they forgot that profit has to be added on top.

Track your actual job costs against your bids to see if your overhead rate is working. If you consistently come in over budget on the overhead portion, the rate needs adjustment. Treasure Valley bookkeeping services that understand construction accounting can help you build job cost reports that show whether your bids are covering what they should.