CFA Level I Exam · Analyzing Income Statements

Common-Size Income Statement and Profitability Margins

Updated 7 October 2026 · Fact-checked

A common-size income statement divides every line item by revenue, so each line shows as a percentage of sales. This is vertical analysis. Gross, operating and net margin are the main results. You use them to compare profitability across periods and between companies of different sizes.

Understand Common-Size Analysis and Profitability Ratios

Raw income statements are hard to compare. A company with revenue of $5 billion and one with $500 million cannot be judged by their profit amounts alone. Common-size analysis fixes this by putting everything on the same scale.

In a vertical common-size income statement, you divide each line item by revenue (net sales) in the same period. Revenue becomes 100%. Cost of sales, operating expenses, interest, tax and net income each become a percentage of revenue. Read down the column and you see where each dollar of sales goes.

The margin ratios are specific lines from this statement. Gross profit margin shows what is left after direct costs. Operating profit margin shows what is left after operating costs such as selling and administrative expenses. Net profit margin shows what is left for owners after all expenses, including interest and tax.

You use the percentages in two ways. Across time, you see if costs are rising faster than sales. Across companies, you see differences in pricing, cost control and business model. A falling gross margin points to pricing pressure or higher input costs. A stable gross margin with a falling operating margin points to rising overhead.

Common-size data show structure, not size. A company can have a higher margin and still earn less in absolute terms. Also check that the companies use similar accounting choices, such as inventory methods, before you compare.

Key formulas to remember

Common-size line item: Line item % = Line item ÷ Revenue × 100; Vertical analysis. Revenue is the base, so revenue = 100%.
Gross profit margin: Gross profit ÷ Revenue, where Gross profit = Revenue − Cost of sales; Measures profit after direct production costs only.
Operating profit margin: Operating profit (EBIT) ÷ Revenue; Operating profit = Gross profit − operating expenses. It is before interest and tax.
Pretax margin: Earnings before tax (EBT) ÷ Revenue; EBT = EBIT − interest expense. Includes the effect of financing costs.
Net profit margin: Net income ÷ Revenue; Net income is after tax. Use net income as given unless the question says to use income attributable to owners.
Change in margin: Margin change (in percentage points) = Margin year 2 − Margin year 1; Report as percentage points, not as a percentage.

How to solve Common-Size Analysis and Profitability Ratios questions

Use this method for any question on common-size statements or margins.

1Identify the base. For a vertical income statement it is revenue (net sales) of the same period.
2Write down each line you need: revenue, cost of sales, operating expenses, interest, tax, net income.
3Build the missing subtotals. Gross profit = revenue − cost of sales. Operating profit = gross profit − operating expenses. EBT = operating profit − interest.
4Divide the required line by revenue. Keep at least one decimal place until the end.
5If comparing periods or firms, subtract margins to get percentage-point differences.
6Interpret: which cost line drove the change? Link a gross margin move to pricing or input costs, and an operating margin move to overhead.
7Check the answer against the three options. Eliminate any that fail a rough check, such as a margin above 100% or a net margin larger than the operating margin without a gain.

Quickest way: Margin first, then eliminate

When to use it: Use this when the question gives amounts and asks for one margin or a comparison, and you have about 90 seconds.

Find revenue and the single numerator you need. Skip other lines.
Divide the numerator by revenue and multiply by 100. On the BA II Plus, press numerator ÷ revenue = then × 100. On the HP 12C, enter numerator, ENTER, revenue, ÷, then 100 ×.
Do a sense check: the margin must be below 100%, and gross ≥ operating ≥ pretax ≥ net in the normal case.
Compare with the three options, which run from smallest to largest. If two options are far apart, a rough mental division is enough.
For trend questions, compare percentages rather than amounts. A cost that grew 8% when revenue grew 10% has fallen as a share of sales.

Common mistakes in Common-Size Analysis and Profitability Ratios

Dividing by the wrong base, such as gross profit or total expenses.
Candidates mix up common-size analysis with other ratios.
Fix: For a vertical income statement the base is always revenue. Net income ÷ revenue, not net income ÷ gross profit.
Using the wrong profit line for operating margin.
Operating profit, EBITDA and EBT sound alike.
Fix: Operating profit is after operating expenses and depreciation, before interest and tax. Build it step by step from revenue.
Reporting a margin change as a percent change.
A move from 20% to 22% gets called 10% instead of 2 points.
Fix: Subtract margins to get percentage points. Use relative change only if the question asks for it.
Concluding that a lower margin means lower profit.
Margins are mixed up with absolute income.
Fix: Common-size figures show structure. Profit in currency units can rise while the margin falls if revenue grows faster.
Comparing companies without checking accounting differences.
Percentages look comparable on the surface.
Fix: Check inventory method, depreciation policy and where costs are classified. These change gross and operating margins.

Worked examples

Example 1

A company reports revenue of $800 million, cost of sales of $520 million, operating expenses of $152 million, interest expense of $18 million and income tax of $22 million. What is the net profit margin? A) 4.5% B) 7.0% C) 11.0%

Show the solution

Gross profit = 800 − 520 = $280 million.
Operating profit = 280 − 152 = $128 million.
EBT = 128 − 18 = $110 million.
Net income = 110 − 22 = $88 million.
Net margin = 88 ÷ 800 = 0.11 = 11.0%.
Only 88 ÷ 800 = 11.0% matches. A (4.5%) and B (7.0%) do not correspond to the computed net income.

Answer: C) 11.0%

Example 2

In Year 1, a retailer had revenue of €400 million and cost of sales of €260 million. In Year 2, revenue was €500 million and cost of sales was €340 million. Which statement is correct? A) Gross margin fell by 3.0 percentage points B) Gross margin was unchanged C) Gross margin rose by 3.0 percentage points

Show the solution

Year 1 gross profit = 400 − 260 = €140 million. Gross margin = 140 ÷ 400 = 35.0%.
Year 2 gross profit = 500 − 340 = €160 million. Gross margin = 160 ÷ 500 = 32.0%.
Change = 32.0% − 35.0% = −3.0 percentage points, a fall of 3.0 points.
Option A states a 3.0-point fall, which matches. Option B is wrong because the margins differ. Option C has the wrong direction.

Answer: A) Gross margin fell by 3.0 percentage points

Exam tips

Questions often give amounts and ask for a percentage. Build the subtotals first, then divide once.
Expect interpretation items: a falling gross margin with a stable operating margin means other costs were cut, and the reverse points to overhead growth.
Watch the wording percentage points versus percent. Options may differ only in this.
Use the option order. Options run from smallest to largest, so a rough division often removes two choices.
Use IFRS line names. Cost of sales, finance costs and profit for the year are common labels.

Practice questions from Analyzing Income Statements

Common-Size Analysis and Profitability Ratios in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Common-Size Analysis and Profitability Ratios: frequently asked questions

What is a common-size income statement?

It restates each income statement line as a percentage of revenue. Revenue is 100%. This lets you compare firms of different sizes and the same firm across years.

What is the difference between vertical and horizontal analysis?

Vertical analysis divides every line by a base in the same period, usually revenue. Horizontal analysis compares each line with the same line in a base year, to show growth or trend.

How do I calculate gross, operating and net margin?

Gross margin is gross profit ÷ revenue. Operating margin is operating profit ÷ revenue. Net margin is net income ÷ revenue. Each uses revenue as the denominator.

Can net margin be higher than operating margin?

Yes, but only if there are net gains below operating profit, such as investment income or a tax credit that exceeds interest and other costs. Normally net margin is lower.