The Job That Looked Fine Until You Divided by the Wrong Number
A shop quotes a five-axis job at $85 an hour and it comes in on budget. The same week, a simple two-axis bracket job quoted at the same $85 an hour loses money, and nobody on the floor can say why — the operator ran to print, the setup wasn't unusual, the material cost matched the quote. The gap isn't in the labor. It's in the rate itself: a single shop-wide hourly number is being asked to cover a $400,000 five-axis machine and a $60,000 manual mill with the same overhead load, and it can't do both accurately. This is what a burden rate is supposed to fix, and it's also where most shops get the math close enough to pass a gut check and wrong enough to erode margin quietly, job after job.
This article walks through the actual method: what goes in the overhead pool, how to pick an allocation base, how to divide the two, and the specific mistakes — mixing pools, ignoring per-work-center differences, forgetting to true up — that make an otherwise correct-looking calculation useless in practice.
What a Burden Rate Actually Pays For
A burden rate — sometimes called a labor burden rate or an overhead absorption rate — is the dollar figure per hour (or per unit of whatever base you choose) that spreads a shop's indirect costs across the jobs running through it. Direct labor and direct material get charged straight to a job because they're easy to track: an operator's hours on job 4471, the plate stock that became the bracket. Everything else — the building lease, the insurance, the maintenance tech's salary, the depreciation on the CNC lathe that sat idle for two hours between setups — has to be allocated somehow, because none of it attaches to one job on its own. The burden rate is that allocation, expressed as a rate so it can be added to a labor rate and rolled into a quote.
Understanding labor burden rate manufacturing practice matters here because burden and pure labor cost are often conflated. Labor burden narrowly refers to the employer-side costs stacked on top of a wage — payroll taxes, workers' comp, benefits — while a shop's full burden rate typically also folds in facility and equipment overhead. Which costs belong in the pool is a policy decision, and it's the first place shops diverge.
Step 1: Build the Overhead Pool
Before any division happens, gather every cost that supports production but isn't direct labor or direct material for a specific job. A representative pool includes:
- Facility costs: rent or mortgage, utilities, property tax, facility insurance
- Equipment costs: depreciation, maintenance contracts, calibration
- Indirect labor: supervisors, quality inspectors, maintenance techs, the person entering data from paper travelers
- Consumables not billed to a specific job: cutting fluid, shop supplies, tooling wear that isn't job-specific
- Administrative overhead allocated to the shop floor: a portion of accounting, IT, or ownership time spent on operations
This is the step where overhead allocation manufacturing practice gets inconsistent between shops, because the pool boundary is a judgment call. Some shops include the front-office administrative burden; others carve it out and run it through a separate SG&A markup. Neither is wrong, but the choice has to be consistent from one quoting period to the next, or the rate becomes unusable for comparing job profitability across quarters.
Pick a period — most shops use a fiscal year, some use a rolling twelve months — and total the pool for that period. This is your numerator.
Step 2: Choose an Allocation Base
The denominator is the allocation base: the measure of activity you'll divide the overhead pool by to get a rate per unit of that activity. The three common choices:
Direct labor hours. Total hours worked by production employees across the period. This is the simplest base and works reasonably well in labor-intensive shops where machine cost doesn't vary wildly between jobs.
Machine hours. Total hours machines ran across the period. This base tracks reality better in capital-intensive shops — CNC-heavy operations where a five-axis mill consumes far more overhead per hour (depreciation, maintenance, power) than a manual bandsaw, but both might employ an operator for a similar number of labor hours.
Direct labor dollars. Total direct labor cost (not hours) across the period. Rarely the best choice for a job shop because it embeds wage-rate differences between operators into the allocation, which usually isn't the driver of overhead consumption.
For most CNC machining, sheet metal fabrication, and welding shops, machine hours track overhead consumption more accurately than labor hours, because the equipment — not the person — is what's driving depreciation, power draw, and maintenance cost. But machine-hour tracking requires actually logging machine run time distinct from labor time, which many shops running on paper travelers and QuickBooks simply don't capture. That gap is exactly why so many shops default to labor hours even when it's the less accurate base: it's the number they already have.
This is also the point where a single, shop-wide base starts to break down for shops with mixed equipment — which is covered in the mistakes section below.
Step 3: Calculate the Rate
The formula itself is simple:
Burden rate = Total overhead pool ÷ Total allocation base (for the same period)
Here's a worked example, illustrative for a representative shop and not a real quoted figure. Suppose a shop's overhead pool for the year totals $480,000 (facility, equipment, indirect labor, consumables). The shop logs 12,000 machine hours across all equipment for that year.
$480,000 ÷ 12,000 machine hours = $40 per machine hour
That $40 is added on top of the direct labor rate and direct material cost to build a fully burdened job cost. If a job runs 6 hours on that equipment with a direct labor rate of $32/hour, the job's cost before material is:
(6 hours × $32 direct labor) + (6 hours × $40 burden) = $192 + $240 = $432
This is the mechanism behind a predetermined overhead rate calculation: the rate is set in advance, using a forecast or trailing-period pool and base, and then applied consistently to every job quoted or costed during the following period — rather than recalculated job by job, which would make quoting impossibly slow and inconsistent.
Where Shops Get This Wrong
One rate for every work center. A shop that calculates a single blended burden rate and applies it everywhere is implicitly saying every machine costs the same to run per hour. It doesn't. A five-axis mill with a six-figure price tag and a service contract has a fundamentally different overhead footprint than a manual deburring station. Blending them means jobs that run mostly on cheap equipment are overcharged, and jobs that run mostly on expensive equipment are undercharged — and the undercharged jobs are usually the ones that look fine on paper and lose money in practice, exactly like the five-axis-versus-bracket scenario at the top of this article. The fix is calculating burden per work center: each work center gets its own overhead pool (its share of depreciation, its own maintenance history, its allocated floor space) divided by its own hours.
Never truing up. A predetermined rate is a forecast. If actual overhead or actual hours come in materially different from the period used to set the rate, jobs quoted all year were priced against a number that was already wrong by Q2. Revisit the rate at least annually, and sooner if a major cost changes — a new equipment lease, a rent increase, a shift in headcount.
Confusing burden rate with the full shop rate. Burden rate is one input. The full hourly shop rate a shop quotes to a customer also folds in the direct labor rate and, in most shops, a margin or profit target on top of fully burdened cost. Treating the burden rate alone as the quoting rate undercharges every job by the labor cost embedded in it.
No mechanism to check the rate against reality. A burden rate calculated once a year is a forecast; the only way to know if it's still accurate is comparing what a job was quoted at against what it actually cost once it's done — actual labor hours per operation against the standard the rate assumed. Shops running paper travelers and spreadsheets often can't make that comparison at the job or operation level at all, which is part of why an inaccurate burden rate can go unnoticed for a full fiscal year.
Putting the Rate to Work
Once the burden rate is calculated, per work center, on a base that reflects how that equipment actually consumes overhead, it becomes an input to every quote and every job cost record going forward — until the next true-up. Getting from a burden rate to a defensible, per-work-center hourly shop rate, and then verifying that rate holds up against actual job performance, is covered in more depth in our job costing resource hub.
For shops that want to run this calculation without rebuilding a spreadsheet from scratch, the Shop Rate & Burden Calculator is a downloadable template built around this exact method — overhead pool, allocation base selection, and per-work-center rate output — so the first pass at a defensible rate doesn't start from a blank sheet.
