Why Your Manufacturing Costs Are Wrong: Common Accounting Mistakes
Running a manufacturing business means juggling production schedules, managing suppliers, keeping equipment running, and meeting customer deadlines.
With all that going on, it’s easy to let accounting become an afterthought that something you deal with when tax returns are due or when the bank wants updated figures.
But poor accounting practices creates directly impact your ability to make sound business decisions, price products profitably, and grow sustainably.
Here are the most damaging accounting mistakes I see manufacturing businesses make, and what to do about them.
Using Average Costs for Everything
Many manufacturers calculate a simple average cost per unit by dividing total production costs by units produced. It’s quick, it’s easy, and it tells you absolutely nothing useful.
Average costing hides the truth about individual product profitability. That small batch run that required three hours of setup time? It gets averaged in with your long production runs.
Products with high material wastage rates? Averaged out. Items that tie up expensive machinery for hours? Lost in the numbers.
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When you price based on averages, you might be subsidising loss-making products with your profitable ones without realising it. You’ll accept orders that actually destroy value because the numbers looked acceptable.
Proper cost accounting means tracking costs at the product or job level. You need to know what each SKU actually costs to produce, accounting for its specific material usage, labour requirements, machine time, setup costs, and yield rates. Only then can you make informed decisions about pricing, which orders to pursue, and where to focus production capacity.
Ignoring Setup and Changeover Costs
Setup time is dead time for revenue generation, but it’s very much alive as a cost. Every time you switch between products, you’re paying for machine downtime, labour to reconfigure equipment, test runs, and often material wastage as you dial in the new settings.
These costs are real and substantial, yet many manufacturers either ignore them entirely or spread them so thinly across production volumes that they become invisible.
The result? You treat a 50-unit batch run the same as a 5,000-unit run in your costing, even though the setup cost per unit is drastically different.
Small batch production can be profitable, but only if you account for setup costs properly and price accordingly. When you don’t, you end up accepting small orders at prices that look reasonable on paper but actually lose money once you factor in the true cost of production.
Track your setup times by product or product family. Calculate the labour and material costs involved. Then allocate these costs to the specific batch being produced. Your accounts should reflect the economic reality: small batches cost more per unit to produce.
Treating All Overheads the Same
Manufacturing overhead includes everything from factory rent and equipment depreciation to maintenance, utilities, quality control, and production management salaries. Lumping all these costs together and spreading them across production using a single overhead rate is crude accounting that distorts product costs.
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Different products consume overhead resources differently. One product might require extensive quality testing; another might need minimal inspection. One ties up on an equipment; other runs on basic machinery. Applying the same overhead percentage to all products ignores these differences.
Activity-based costing offers a more accurate approach. You identify what drives each overhead cost such as machine hours, setup frequency, inspection requirements, material movements and allocate costs based on how much each product actually uses those resources.
This doesn’t mean you need elaborate systems or complex calculations for every overhead line. But you should at least separate variable overheads (which change with production volume) from fixed overheads and consider whether different product groups warrant different treatment based on their actual resource consumption.
Poor Inventory Valuation Practices
Inventory valuation affects both your balance sheet and your profit calculations, yet many manufacturers treat it as a year-end compliance exercise rather than an ongoing management tool.
Common problems include failing to write down obsolete stock, using outdated standard costs that don’t reflect current material or labour rates, and not accounting for work-in-progress properly. Some businesses carry inventory at purchase cost without adding the manufacturing costs incurred to transform materials into finished goods.
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When your inventory values are wrong, your gross profit figures are wrong. You might show healthy margins while sitting on a pile of unsaleable stock. Or you might be undervaluing inventory and understating your true profitability.
Regular inventory reviews should be part of your routine, not just an annual event. Update your standard costs when material prices or labour rates change significantly.
Identify slow-moving and obsolete stock promptly and adjust values accordingly. Make sure your WIP valuation includes all costs incurred, materials, labour, and allocated overheads.
Failing to Track Yield and Wastage
Material wastage, production rejects, and yield rates have a direct impact on your costs, yet many manufacturers don’t track these systematically at the product level. You might know your overall material spend, but do you know which products or processes generate the most waste?
Some level of wastage is inevitable in manufacturing. Offcuts, startup waste, quality rejects. But without tracking it by product or process, you can’t identify problems, make improvements, or cost products accurately.
A product with a 15% reject rate costs substantially more to produce than one with a 2% reject rate, even if the good units look identical.
If your costing doesn’t reflect this, you’re underestimating production costs and likely under-pricing the product.
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Build yield and wastage tracking into your production recording. Calculate expected waste based on historical data and include it in your standard costs. Review variances regularly to identify where actual performance deviates from expectations. This visibility drives both better costing and operational improvement.
Not Separating Production from Period Costs
Manufacturing costs should be matched to the products you make. Period costs like sales, marketing, and administrative expenses belong in the period they occur. Mixing these up distorts your understanding of production profitability and makes it harder to identify where your business actually makes money.
This matters most when production volumes fluctuate. If you’re spreading period costs across production units, a quiet month makes every unit look more expensive, while a busy month makes everything look cheaper. Neither reflects reality.
Keep your cost accounting focused on production costs: direct materials, direct labour, and manufacturing overheads. Treat selling, general and administrative expenses separately as period costs. This gives you clean gross margin figures that actually tell you about production efficiency and product profitability, independent of how much you’re spending on the business infrastructure.
Moving Forward
These mistakes happen because production demands get immediate attention while accounting wait. But poor accounting catches up with you in missed opportunities, unprofitable orders accepted, and profitable ones turned down because the numbers didn’t look right.
Getting your manufacturing accounting right isn’t about complexity for its own sake. It’s about having cost information you can actually use to make decisions: which products to push, how to price custom orders, where to invest in capacity, which customers are truly profitable.
If you’re recognising some of these issues in your own business and want to develop cost accounting that actually reflects manufacturing reality, that’s exactly what I help industrial businesses with.
Get in touch to discuss how proper cost accounting can give you clearer visibility of your true production costs, product profitability and financial management.
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About the Author
Written by Yesim Tilley Founder of Skynet Accounting is a chartered accountant with over 20 years of experience supporting manufacturing and engineering businesses across the UK. Specialising in cost analysis, product costing, and financial strategy, she helps industrial businesses understand their numbers and make more profitable decisions. Skynet Accounting provides tailored finance, compliance, and taxation support designed specifically for the manufacturing and engineering sector.