Updated for the 2026-2027 CFA® Level I curriculum.
A common-size income statement restates every line item as a percentage of revenue. This turns raw dollar figures into comparable numbers, so you can measure a company against its own history or against competitors of different sizes. CFA Level I tests both the mechanics of building this statement and your ability to read what the resulting ratios say about a company's cost structure and profitability.
Quick Answer
A common size income statement divides each income statement line by revenue, showing every item as a percentage of sales. The three main ratios it produces are gross profit margin, operating margin, and net profit margin. These ratios let you compare profitability across companies of different sizes or track a single company's cost structure over time, regardless of changes in revenue scale.
Key Takeaways
A common-size income statement expresses every line item as a percentage of revenue, not as a dollar amount.
The three core ratios are gross profit margin, operating margin, and net profit margin.
Gross margin reflects cost of goods sold relative to revenue; it signals pricing power and production efficiency.
Operating margin adds operating expenses into the picture, showing how well a company controls overhead.
Net profit margin captures the bottom line after interest, taxes, and all other charges.
Common-size analysis is most useful when comparing trends across years or companies of different sizes.
What You Need to Know for CFA Level I
The LOS asks you to evaluate performance, not just calculate percentages. Expect questions that require interpretation, not just arithmetic.
You must know how to construct a common-size income statement by dividing each line by revenue.
You must calculate and interpret gross profit margin, operating margin, and net profit margin.
Know the boundary with EPS: common-size ratios measure profitability as a percentage of sales, while EPS measures profit per share. They answer different questions.
Watch for the trap of treating a rising dollar figure as good news when the common-size percentage is actually falling.
Margins should be read in context. A declining gross margin with a rising operating margin tells a different story than both declining together.
What Is a Common-Size Income Statement?
A common-size income statement takes the standard income statement and restates each line as a percentage of total revenue. Instead of asking "how much did cost of goods sold increase in dollars," you ask "did cost of goods sold grow faster or slower than revenue."
This matters because dollar figures alone can mislead you. A company with revenue of $10 million and net income of $1 million looks similar in raw terms to a company with revenue of $100 million and net income of $9 million. Common-size analysis shows the first company earns a 10% net margin while the second earns only 9%, even though the second company is ten times larger.
Why Analysts Use Common-Size Statements
Common-size statements solve two comparability problems:
Size differences
Comparing a small company to a large competitor in dollar terms tells you little. Comparing their margins tells you which one runs a more efficient operation.
Time differences
A single company's revenue grows or shrinks over time. Common-size statements strip out that growth so you can see whether costs are rising faster or slower than sales.
Components of the Income Statement Used in Common-Size Analysis
To build a common-size income statement, you need the standard components already found on the income statement:
Revenue (the base for every percentage)
Cost of goods sold (COGS)
Gross profit (revenue minus COGS)
Operating expenses (SG&A, R&D, depreciation tied to operations)
Operating income (gross profit minus operating expenses)
Non-operating items (interest expense, interest income)
Pretax income
Income tax expense
Net income
Each of these lines is divided by revenue to produce the common-size version. No other inputs are required.
Building the Common-Size Income Statement
The formula is the same for every line item.
where:
Line Item: the dollar value of any income statement line (COGS, operating expenses, net income, and so on),
Revenue: total net revenue or net sales for the period, used as the denominator for every line.
Revenue itself always equals 100% in a common-size income statement. Every other line is measured against it.
The Three Core Income Statement Ratios
Three useful profitability measures follow directly from common-size income statement analysis.
where:
Gross Profit: revenue minus cost of goods sold,
Operating Income: gross profit minus operating expenses (sometimes called EBIT when no other non-operating items are present), and
Net Income: profit remaining after interest, taxes, and all other expenses.
What Each Ratio Tells You
Ratio | What It Measures | Rises When |
|---|---|---|
Gross profit margin | Pricing power and direct production cost control | Revenue grows faster than COGS, or the company raises prices without raising costs proportionally |
Operating margin | Control over operating expenses beyond production costs | Operating expenses grow slower than revenue |
Net profit margin | Overall profitability after every expense, including interest and tax | Non-operating costs (interest, tax) stay flat or fall while revenue grows |
A gap between gross margin and operating margin points to overhead cost control. A gap between operating margin and net margin usually points to financing costs or tax rate changes, not operating performance.
Working Example
Scenario: Orion Robotics reports the following figures for two consecutive years.
Line Item | Year 1 (millions of dollars) | Year 2 (millions of dollars) |
|---|---|---|
Revenue | 500 | 600 |
Cost of goods sold | 300 | 390 |
Gross profit | 200 | 210 |
Operating expenses | 120 | 132 |
Operating income | 80 | 78 |
Interest expense | 10 | 12 |
Pretax income | 70 | 66 |
Income tax expense | 20 | 18 |
Net income | 50 | 48 |
Step 1: Build the common-size income statement.
Line Item | Year 1 (percentage of revenue) | Year 2 (percentage of revenue) |
|---|---|---|
Revenue | 100.0% | 100.0% |
Cost of goods sold | 60.0% | 65.0% |
Gross profit | 40.0% | 35.0% |
Operating expenses | 24.0% | 22.0% |
Operating income | 16.0% | 13.0% |
Interest expense | 2.0% | 2.0% |
Pretax income | 14.0% | 11.0% |
Income tax expense | 4.0% | 3.0% |
Net income | 10.0% | 8.0% |
Step 2: Calculate the three core margins.
Step 3: Interpret the results.
Revenue grew 20% from Year 1 to Year 2, and net income in dollar terms only fell slightly, from $50 million to $48 million. A quick glance at dollar figures might suggest stable performance. The common-size statement tells a different story. Gross margin fell from 40% to 35%, meaning cost of goods sold grew faster than revenue.
Operating margin fell from 16% to 13% despite operating expenses growing only 10%, below revenue growth of 20%. Better overhead control partly offset the larger increase in cost of goods sold. Net margin dropped from 10% to 8%. Orion Robotics is growing its top line but losing profitability on every dollar of sales. An analyst would flag rising input costs or pricing pressure as the likely cause and look for it in the notes to the financial statements.
Common Exam Traps
Confusing dollar growth with margin improvement
A company can show rising net income in dollars while its net profit margin falls, if revenue grows faster than profit. Always check the percentage, not just the dollar trend.
Mixing up gross margin and operating margin drivers
Gross margin reflects COGS only. Operating margin reflects COGS plus operating expenses. A falling operating margin with a stable gross margin points to overhead problems, not production cost problems.
Treating common-size ratios as a substitute for EPS analysis
Common-size margins measure profitability as a percentage of revenue. EPS measures profit allocated per share outstanding. These answer different questions and are tested separately.
Ignoring the denominator
Every common-size percentage uses revenue as the base. A total-assets denominator is generally used for common-size balance sheets; a total-expenses denominator would be a different expense analysis, not the income statement version this page covers.
Assuming a higher margin always means better performance
A high gross margin paired with a very low operating margin can signal a bloated cost structure. Read all three margins together before forming a conclusion.
Practice Question
Harbor Fitness reports revenue of $240 million and cost of goods sold of $156 million for the current year. Last year, revenue was $200 million and cost of goods sold was $120 million. Based on this information, which statement is most accurate?
Gross profit margin improved from last year to the current year.
Gross profit margin declined from last year to the current year.
Gross profit margin stayed the same because gross profit increased in dollar terms.
Correct Answer: Option B
Gross margin fell from 40.0% to 35.0%, even though gross profit in dollar terms rose from $80 million to $84 million.
Cost of goods sold grew faster than revenue (30% increase in COGS versus 20% increase in revenue), which pulled the margin down despite higher dollar profit.
Option A: Assumes rising dollar profit automatically means rising margin. It does not, because revenue and COGS did not grow at the same rate.
Option C: Confuses a dollar increase in gross profit with a stable percentage margin. The percentage changed even though the dollar amount grew.
Continue Your CFA Level I Prep With KeyPoint
Use structured lessons, practice questions, mock exams, and progress tracking to focus on the time you have left
FAQs About Common-Size Income Statements and Income Statement Ratios
What is the common-size income statement formula?
Divide each income statement line item by total revenue, then multiply by 100 to express it as a percentage. Revenue always equals 100% in this format.
What is the difference between gross margin and net profit margin?
Gross margin only accounts for cost of goods sold. Net profit margin accounts for every expense, including operating costs, interest, and taxes. Net margin is usually lower, but significant non-operating gains or tax benefits can produce exceptions.
Why do analysts use common-size income statements instead of raw dollar figures?
Raw dollars make it hard to compare companies of different sizes or to track a single company's cost structure as revenue changes over time. Common-size percentages remove the size distortion.
Can a company have rising revenue and a falling net profit margin at the same time?
Yes. This happens when costs grow faster than revenue. It is a common pattern tested on the exam and signals weakening cost control even as sales grow.
Is the common-size income statement the same as a common-size balance sheet?
No. A common-size income statement uses revenue as the base for every line. A common-size balance sheet uses total assets as the base. They answer different analytical questions.