How this instrument works
Cost of doing business, as this sheet defines it, is the share of revenue already spoken for once fixed overhead and a variable rate are both counted. The formula treats the two cost types differently on purpose: fixed costs enter as a flat dollar figure that ignores revenue entirely, while variable costs are modeled as a percentage of revenue rather than a per-unit price times a quantity sold. That percentage-of-sales approach is how cost of goods sold, commissions, and card fees usually get quoted in a financial plan or a franchise disclosure document — as a rate against sales, not a per-item cost against a unit count.
A person building a one-page projection reaches for this shape of arithmetic constantly: an owner sketching next year's numbers from last year's cost rate, a lender skimming a loan applicant's plan for a plausible expense structure, or a franchisee comparing a location's total cost ratio against a same-brand benchmark. None of those readers has a unit count handy — they have a revenue figure and a rule-of-thumb percentage, and this sheet turns both straight into a dollar total and a ratio without requiring a bill of materials.
Because fixed costs sit in dollars while variable costs sit in percent, the resulting ratio is not a constant property of the business — it moves whenever revenue does, even if nothing about spending discipline changed. Doubling revenue on the same fixed-dollar figure and the same variable rate lowers the ratio, because the fixed slice gets spread over a bigger number while the variable slice stays proportional. Read the ratio as a snapshot at one specific revenue figure, not as a fixed constant to be carried into a very different sales scenario unchanged.
- Enter one period's total sales into Revenue, $ — the figure the ratio will be measured against.
- Add up rent, salaries, insurance, and anything else billed on a schedule regardless of sales, and enter that total into Fixed costs, $.
- Set Variable costs, % of revenue to your best rate for costs that scale with sales — cost of goods sold, commissions, card processing.
- Read Variable costs and Total costs for the dollar figures, and Total cost as % of revenue for the share of each sales dollar already spent.
Worked example — $200,000 in revenue, a 30% variable rate
Take a business posting $200,000 in revenue for the period, with $50,000 of fixed costs covering the lease, salaries, and insurance that come due whether sales were strong or slow, and a variable rate of 30% of revenue covering materials, commissions, and card fees that move with each sale. Variable costs work out to 200,000 times 30%, or $60,000, so total costs land at 50,000 plus 60,000, or $110,000, and dividing that into revenue puts the cost ratio at 110,000 divided by 200,000 times 100, or 55%.
Fifty-five cents of every revenue dollar is already spoken for before taxes, interest, or an owner draw enter the picture, leaving a 45% margin to work with above the line this sheet measures. Because $50,000 of that total sits in dollars rather than percent, the ratio would shift if revenue climbed while fixed costs and the 30% rate held steady — a $400,000 month on that same cost structure prices out closer to 42.5%, not 55%, purely because the fixed slice gets spread over twice the sales.
Questions
Why does the cost ratio change even though my fixed costs stayed the same?
Because fixed costs sit in dollars, not percent. Variable costs scale automatically with revenue, but a flat fixed figure does not grow when sales do, so it becomes a smaller share of a larger number and the ratio falls as revenue rises — with no change in spending discipline behind it. Watch the ratio at more than one revenue level before treating it as a fixed trait of the business.
How is this different from a break-even calculation?
Break-even works backward from a zero-profit target to find the sales volume or revenue that clears fixed costs, using a price and a per-unit cost as inputs. This sheet works forward from a revenue figure already on hand, applying a percentage-of-sales estimate for variable costs, and reports the cost ratio at that one scenario — it never solves for a threshold, only measures a specific point.
Why enter variable costs as a percentage of revenue instead of a per-unit cost?
Because plenty of real costs move with sales dollars rather than a countable unit — commissions, card processing fees, freight priced as a share of order value, and cost of goods sold quoted as a ratio in a financial plan. A percentage-of-revenue rate suits a service business without a single unit, or a quick projection built from last year's cost rate rather than a fresh materials buildup.
What counts as a normal cost ratio for a small business?
There is no universal figure — it depends heavily on the industry. A software business with light delivery costs might run 30 to 40%; a restaurant tracking food, labor, and occupancy together commonly lands near 60 to 65%; a wholesale distributor can clear 90% because inventory dominates its spending. Compare the result against your own trailing months or a same-industry figure, not a generic target.
Is the cost ratio the same thing as my profit margin?
It is close to the mirror image, not an identical figure. Cost ratio plus profit margin only sum to 100% of revenue if every real cost is captured inside Fixed costs and Variable costs, and only before taxes, interest, and any owner draw are subtracted. A 55% cost ratio implies roughly a 45% margin at this stage, not a final after-tax number.
Can the variable cost percentage go above 100%?
The sheet computes it if entered, but a rate past 100% means variable costs alone already exceed the revenue that produced them, before fixed costs are even added — a structure that loses money on every sale regardless of volume. Check the figure against actual cost of goods sold before trusting the output; entering 300 instead of 30 is a common source of this result.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.