What is Indirect Manufacturing Cost?
Indirect manufacturing cost covers every expense a supplier incurs to run their plant, minus what goes into the finished product. This includes utilities, supervision, taxes, overhead, and indirect materials like spare parts and conveyor belts. None of this ends up in the part you’re buying, but the costs still have to be covered by the price you pay.
Indirect manufacturing cost matters because it’s a function of throughput: fixed overhead divided by units produced. When volume falls, the indirect cost per part rises, even though nothing about the product has changed. This makes indirect cost useful data for buyers—not as a line to attack, but as a read on what’s happening inside the supplier’s operation.
What should purchasing managers do with indirect manufacturing cost?
Calculating a supplier’s indirect cost from the outside is very difficult to achieve, to say the least. You’d need to know the full cost of running the plant, every other customer they serve, and the throughput across all of them.
When preparing a should-cost analysis, a more useful approach is to group indirect cost with overhead and profit margin to estimate the gross margin. Treat this figure as a constant between negotiations. What changes between cycles is the direct material cost, and that number is knowable. If the part you’re buying is made from steel or a plastic resin, you can track how that material’s price has trended since you last negotiated and price the part from there.
The diagnostic value shows up when a supplier breaks the pattern. Suppliers almost always cite direct material increases when they push for a price rise, and stay quiet when those material costs fall. When a supplier points to indirect costs as justification for a price increase, ask them why. Have they lost business? Dropped a shift? Are they running two where they used to run three?
A plant tour is the most efficient way to check if a change in indirect costs is a result of operational challenges. Walk the floor and look at throughput, scrap piles, and shift patterns. If the plant seems less busy than it was, that may explain the price hike. It might also signal that it’s time to look at other suppliers.
Key Considerations
- Indirect manufacturing costs should stay relatively constant between negotiations. If a supplier claims these costs have risen, the explanation usually points to a volume or efficiency problem on their side. This isn’t a cost you should absorb.
- Don’t try to reverse-engineer indirect cost on its own. Group it with overhead and profit margin as a single gross-margin bucket. Focus your analysis on direct materials, which can be tracked and verified.
- A plant tour is the most reliable way to test a supplier’s indirect cost story. Shift patterns, scrap piles, and throughput will tell you whether the operation is running the same way it was during your last visit.
