What factors affect our choice of method to treat overallocated or underallocated manufacturing overhead?

Question

What factors affect our choice of method to treat overallocated or underallocated manufacturing overhead ?

Thanks.

Answer 1

The choice comes down to three factors that actually matter in practice:

1. Materiality. This is the most important factor. If the variance is small (typically under 5-10% of total overhead), writing it off to COGS makes sense. Any larger variance should result in proration or the result is materially misstating inventory values and COGS. The threshold number of 5-10% is chosen because at higher amounts, actual decision-making is affected.

1. Where the inventory actually is. If 90% of your production has already shipped and sits in COGS, proration and write-off produce nearly identical results. But if you're sitting on substantial WIP or finished goods inventory, writing off a large variance to COGS is not accurate and it misrepresents what those assets cost to produce. You're front-loading or back-loading expense recognition based on convenience rather than economics.

1. Why the variance exists. This gets ignored too often. Random fluctuation from normal capacity variations can be treated as a period cost. But if variances stem from systematic issues (wrong cost drivers, bad rate estimation, significant volume deviation), there is a forecasting problem that won't fix itself. Continuing to use the same allocation method without addressing root causes will perpetuate the eror. Sometimes the answer isn't "how do we allocate this variance" but "why do we keep generating these variances?"