Not all overhead behaves the same way month to month, and knowing which category a cost falls into changes how you plan for and manage it.
Fixed overhead
Stays the same regardless of business activity — rent, insurance premiums, salaried staff. Predictable, but doesn’t shrink automatically during a slow month.
Variable overhead
Moves with business activity — shipping supplies, hourly labor tied to volume, transaction fees. Naturally scales down during slower periods, which offers some built-in protection.
Semi-variable overhead
Has a fixed base plus a variable component — a phone plan with a base fee plus usage charges, utilities with a connection fee plus consumption cost.
Why the distinction matters practically
During a slow period, variable costs adjust on their own, but fixed costs don’t — which is exactly why fixed overhead is usually the first thing to scrutinize when cash flow tightens, since it keeps accruing regardless of revenue.
A worked example
A business carries $8,000/month in fixed overhead — rent, insurance, salaried staff — plus $3 per unit in variable overhead like packaging and hourly labor. At 500 units sold, total overhead is $8,000 + (500 × $3) = $9,500, or $19 per unit. If volume drops to 300 units in a slow month, fixed overhead stays at $8,000 but variable overhead falls to $900, for a total of $8,900 — now $29.67 per unit. The fixed portion doesn’t care how many units you sold; the variable portion does the adjusting for you.
Where overhead typically lands as a share of revenue
- Service businesses: commonly 10–20% of revenue.
- Retail: commonly 20–30%.
- Manufacturing: commonly 25–35%.
- Professional services (agencies, consultancies): often 50–70%, since headcount is the product.
- SaaS: often as low as 5–15%, given minimal marginal cost per customer.
Above roughly 35% of revenue in most non-services industries is generally a signal to review the cost base.
Common mistakes
- Treating semi-variable costs as purely fixed, which hides gradual cost creep (a utility bill or software plan that scales with usage) until it’s already large.
- Not stress-testing which costs would actually shrink in a 20% revenue drop — many “variable” costs turn out to be stickier than expected.
- Budgeting overhead as one lump figure instead of the three categories, which makes it impossible to tell whether a slow month is a cash-flow problem or a structural cost problem.
A quick exercise
List your monthly overhead line by line and mark each as fixed, variable, or semi-variable. Total the fixed column. That number is roughly your minimum monthly burn regardless of sales — the figure that matters most when planning for a slow season.
About the Author
Oliver K.G.
Oliver K.G. has 8+ years in pricing strategy and has helped 200+ Amazon FBA sellers, dropshippers, and small business owners optimise their profit margins. He built BizMargin to make gross margin and pricing calculations instant and free. He writes on pricing strategy, gross margin optimisation, and profitability for e-commerce and retail businesses.