What is an overhead rate calculation?
An overhead rate calculation takes everything an agency spends that is not tied to a client job and expresses it as a rate: per billable hour, or as a percentage of direct labor cost. The output is a single number that can be added to the cost of every hour sold, so that the price of a project carries its fair share of the rent, the software, the admin team and the unpaid pitching. It is the bridge between the business's fixed costs and the price of its work.
The calculation is simple; the inputs are the hard part. It needs an honest overhead total, which means counting non-billable people and non-billable time, and an honest billable hours total, which means timesheets that were actually filled in.
Why it matters
Why overhead rate calculation matters
Every estimate an agency sends is built on an internal rate, and the internal rate is built on the overhead rate. If the overhead rate is wrong, every estimate is wrong by the same amount in the same direction, and the agency will not find out until the year-end accounts. Agencies that skip the calculation tend to price from salary cost plus a margin, and discover that the margin went to the landlord. Agencies that do it know the gross margin each job needs, can see immediately what a new hire or a new office does to their prices, and can tell a client honestly why a senior day costs what it does.
It also tells the agency when it is drifting. An overhead rate that rises year on year while revenue is flat is overhead growing faster than the work, and that is the earliest warning most agencies get.
In practice
How overhead rate calculation works in practice
- 01
Choose a period, usually the last full year. Separate direct costs (everything coded to client jobs, including staff time on them) from indirect costs (everything else). Total the indirect costs, making sure non-billable salary time, the owner's time and pitching are in. Pull total billable hours from the time-tracking system, or total direct labor cost from the same source if the percentage form is being used. Divide.
- 02
Add the result to the loaded cost of each role, add the target margin, and the internal rate is set. Record the inputs so the calculation can be repeated the same way next year, then repeat it: annually at least, and whenever headcount, premises or the software stack change meaningfully. Compare each year's rate to the last and ask what moved it.
Watch out
What people get wrong about overhead rate calculation
Using budgeted figures. A planned overhead divided by hoped-for billable hours gives a rate for an agency that may never exist; the calculation needs actuals. The second mistake is forgetting that the denominator is billable hours, not hours worked, which flatters the rate and underprices the work. The third is treating it as a finance exercise and keeping the result from the producers who estimate, who are the only people who can actually use it.
The fourth is doing it once. Overhead and utilization both change every year; the rate is a snapshot and should be retaken.
