Costs & Margins

COGS vs operating expenses

The two big cost buckets, where they sit, and what they tell you.

Below the revenue line sit two broad families of cost. Cost of goods sold (COGS) — sometimes called cost of revenue or cost of sales — is the direct cost of producing what you sold: materials, direct labour, and the manufacturing or service-delivery costs tied to each unit. Operating expenses are the costs of running the business that aren't tied directly to a unit of product: selling, general and administrative (SG&A) costs, research and development (R&D), marketing, and overhead.

The order matters because the income statement is a waterfall. Revenue minus COGS gives gross profit. Gross profit minus operating expenses gives operating income (EBIT). Each subtotal answers a different question: gross profit asks 'how profitable is the product itself?', while operating income asks 'how profitable is the business once you've paid to run it?'

Why analysts separate the two COGS tends to move with volume; operating expenses often contain a large fixed component. Splitting them is the first step to understanding how a business will behave when revenue changes — which is the whole point of this unit.

Fixed vs variable, and three ways to forecast

Match the forecasting method to how the cost actually behaves.

Every cost behaves in one of two ways. Variable costs scale with activity — sell twice as many units and they roughly double. Fixed costs stay put across a range of volume — rent, a headquarters, a baseline engineering team. Most real lines are a blend (a 'semi-variable' cost), but classifying the dominant behaviour tells you how to forecast it.

Three forecasting methods

• Percentage of revenue — best for variable costs like COGS. Hold the ratio (or trend it gently) and the cost scales with the top line automatically.
• Absolute amount — best for fixed costs like rent or a known overhead budget. Set the dollar figure directly; it doesn't flex with revenue.
• Step change — best for costs that are fixed within a range but jump when you cross a threshold: a new plant, a new distribution centre, a hiring wave.

Forecast cost = Revenue × (Cost ÷ Revenue ratio)The ratio is usually anchored to the historical average, then adjusted for scale, mix, or efficiency. This is the default for COGS.

Don't put fixed costs on a % of revenue If you forecast a fixed cost as a percentage of revenue, you accidentally make it variable — it will balloon in the bull case and vanish in the bear case. That single mistake erases operating leverage from your model and quietly distorts every margin.

1. Pull the historical cost line and divide it by revenue each year to see whether the ratio is stable (variable) or drifting as revenue grows (fixed component).
2. If the ratio is roughly flat, forecast as a percentage of revenue.
3. If the dollar amount is steadier than the ratio, forecast it as an absolute figure.
4. If you expect a discrete jump — a new facility or a major hire — layer in a step change in the year it occurs.

Gross margin and operating margin

Turn the cost base into the two margins every analyst watches.

Margins translate raw costs into a percentage that is comparable across years and across companies. The two that matter most in this unit are gross margin and operating margin. Gross margin reflects pricing power and production efficiency; operating margin reflects the whole operating model, including the overhead it takes to run the business.

Gross margin = (Revenue − COGS) ÷ Revenue = Gross profit ÷ Revenue

Operating margin = EBIT ÷ RevenueEBIT = Gross profit − operating expenses. Operating margin is the cleanest read on core profitability before financing and tax.

Reading the trend is as important as the level. A gross margin that creeps up year after year suggests improving pricing or scale economies; one that erodes suggests rising input costs or discounting. Always compare your forecast margins to the company's own history before you trust them — a forecast that quietly assumes a margin the company has never achieved is a red flag.

Margins are derived for you The Ratios tab computes gross and operating margins from the company's audited EDGAR history and plots the trend automatically. Your job shifts from building the formula to judging whether the assumption is reasonable against the real track record.

Operating leverage

Why a fixed-cost base magnifies margin swings when revenue moves.

Operating leverage is the payoff of everything in this unit. When a company carries a large fixed-cost base, each extra dollar of revenue costs little to serve, so most of it falls through to operating income — margins expand as revenue grows. The same lever works in reverse: when revenue falls, the fixed costs don't, so margins collapse faster than the top line. A high-fixed-cost business is a margin amplifier in both directions.

DOL = % change in operating income ÷ % change in revenueA DOL of 2 means a 10% rise in revenue produces a 20% rise in EBIT. The more fixed the cost base, the higher the DOL.

Leverage is risk and reward at once High operating leverage is wonderful in an upturn and brutal in a downturn. Modelling it correctly — fixed costs as fixed, variable costs as variable — is what makes your bull and bear cases honest instead of cosmetic.

See leverage live On the Ratios tab, the margin trend and the DuPont decomposition update as you flex a revenue assumption. Push revenue up and watch operating margin expand more than proportionally — that visible amplification is operating leverage at work.