How do you calculate marginal profit?

How does marginal profit differ from contribution margin?

Contribution margin is the contribution towards covering costs. In management accounting, contribution margin means revenue minus variable costs. It is also referred to as contribution, or the amount available to cover fixed costs. To calculate it accurately, you need to distinguish it from marginal profit.

The total contribution margin from all projects over a selected period goes towards covering rent, salaries, accounting, communications, software, and other fixed operating costs for the same period. In a simplified model in which variable and fixed cost categories include all operating expenses for one period, the amount left after deducting them is operating profit before finance costs and income tax. Each project contributes towards covering shared costs; whether the full amount is covered is assessed across all projects together.

Marginal profit is the increase in profit from one additional unit of output. In economics, it is calculated as marginal revenue minus marginal cost: MR − MC. In a project business, the unit used for a scenario calculation could be one more project, one more contract, one more stage of work, or one more day of a crew's work.

What formulas do you use to calculate marginal profit?

For the formulas, agree on the period and the rules for recognising revenue and costs. In construction and renovation, revenue from work performed or services provided is recognised in accordance with the contract terms and accounting rules. Receiving an advance payment does not, by itself, mean that revenue has been recognised. You can read more in the articles on revenue and the difference between revenue and profit.

A project's contribution margin is calculated as follows:

Contribution margin = Revenue − Variable costs.

The share of revenue represented by contribution margin is called the contribution margin ratio. It helps compare projects of different sizes when the same accounting rules are used. The formula applies when revenue is positive; division by zero revenue is undefined:

Contribution margin ratio = (Contribution margin ÷ Revenue) × 100%.

Contribution margin = revenue − variable costs. In the hypothetical example: RUB 1,000,000 − RUB 600,000 = RUB 400,000; contribution margin ratio: (400,000 / 1,000,000) × 100% = 40%. The icons are not to scale, and the coins represent the result of the calculation, not the cash balance in an account. The diagram shows a contribution towards covering fixed costs; the increase in profit from an additional unit is calculated separately.

Marginal profit is the difference between additional revenue and additional costs per unit of increase in output: MR − MC. Here, MR means marginal revenue and MC means marginal cost, including costs associated with expansion. For a finite increase in output, the average increase in profit per unit is written as follows:

Average increase in profit per unit = ΔProfit ÷ ΔOutput, where ΔOutput is greater than zero.

If output increases by 1 unit, such as one order or one project, the marginal effect of that step equals the difference between two scenarios for the same period:

Marginal profit from the next project = Profit with the next project − Profit without the next project.

For a practical calculation, compare the scenarios with and without an additional project, allowing for changes in prices, costs, and the capacity used by other projects. Use the same definition of profit in both scenarios; from here on, we use operating profit. The related concept of operating leverage (in Russian) describes the percentage sensitivity of operating profit to a change in sales for a given cost structure.

How do you calculate marginal profit in practice?

In a project business, marginal profit becomes a practical measure when you calculate the contribution margin of each project separately and model the result of additional output. You can repeat the calculation each month and whenever you review prices, keeping the periods and accounting rules comparable.

Consider a hypothetical example for a selected period: the project work has been completed, revenue of RUB 1,500,000 has been recognised under the accounting rules, and the variable costs attributable to it for the same period are RUB 1,000,000. Contribution margin is RUB 500,000. This is the project's contribution towards covering fixed operating costs for the relevant period. Total contribution margin in excess of those costs forms operating profit. Net profit also depends on the results of financing and other activities, and on taxes; the cash balance in the account is calculated separately.

The next question is how operating profit will change if you take on one more project. To answer it, compare two scenarios, including every change in revenue and costs caused by that decision.

1. Step 1. Define the unit of output and the comparison period. In a construction business, this could be a project or a stage of work. Compare units that are equivalent in substance, or calculate a separate scenario for the particular project.
2. Step 2. Determine revenue for that unit under your management accounting rules. Check what work has been performed and what revenue should be recognised in the selected period; account for the timing of payment receipts separately.
3. Step 3. Collect the variable costs for the unit: piecework pay that varies with output, subcontracting, delivery, consumables, and materials. Classify each item according to its actual cost behaviour within the range being considered.
4. Step 4. Calculate contribution margin: revenue − variable costs.
5. Step 5. Check whether the next unit will require additional fixed costs, such as a second site supervisor, warehouse rental, or a full-time accountant. If capacity is limited, account for the new project's effect on other projects, including the possibility of displacing another order.
6. Step 6. Calculate the marginal effect of the next project: operating profit with the next project − operating profit without it over the same period. This equals the additional project's contribution margin if all other prices, costs, and project results remain unchanged and there are no additional fixed costs. If fixed costs rise in steps, deduct their increase for the selected period.

Why should you know your marginal profit?

Marginal profit helps with decisions that change the volume and structure of work: taking on a project, offering a discount, hiring someone, investing in advertising, or opening a new business line. For each decision, assess the entire additional result over the selected period.

You can apply this measure to the following management questions.

• Pricing. Compare the contract price with variable costs and the contribution towards covering fixed costs. For a discount, consider its effect on volume and total profit, as well as any increase in costs. The article on price and cost can help.
• Project selection. Two projects with the same revenue can generate different contribution margins because of their scope of work, logistics, and subcontracting. Keep the margin calculation to hand and remember the difference between margin and markup.
• Sales planning and break-even. With a positive contribution margin per comparable unit and known fixed costs for the period, you can estimate the volume needed to cover those costs. For different types of projects, account for the sales mix. Read more in the article on the break-even point (in Russian).
• Growing the team. Hiring can improve management quality and add fixed costs. Comparing scenarios helps you estimate how much additional output, after allowing for its costs, is needed to cover the cost of the hire.
• Unit economics. Knowing the contribution per unit of output makes it easier to compare acquisition channels and assess the economic result of an order. Include acquisition costs without counting the same costs twice. The article on unit economics (in Russian) can help.

Does this measure change, and what affects it?

Both marginal profit and a project's contribution margin can change. With a constant price and variable cost per unit, the contribution margin of that unit remains constant within the relevant range. Its total amount changes with the number of units sold. The additional effect of a project also depends on the changes it causes in fixed costs and the results of other projects.

In practice, four groups of factors affect the measure:

1) Price and how you update it. If variable cost per unit rises while the price stays the same, contribution margin per unit falls. A change in market prices does not, by itself, change the calculation: the actual prices in your contracts and your costs matter. Compare them regularly.

2) The composition of variable costs. Piecework pay, subcontracting, logistics, consumables, and materials can differ even when the measured quantity of work is the same. Contracts with the same revenue can have different contribution margins because of the composition and amount of variable costs.

3) Steps in fixed costs. Moving to additional capacity may require a new employee, a warehouse, or equipment. The resulting fixed costs reduce additional operating profit for the relevant period. Operating leverage (in Russian) describes the percentage sensitivity of total operating profit to sales: near break-even, a small change in sales can produce a large percentage change in a small positive profit. At zero profit, a ratio with profit in the denominator is undefined. This effect does not, by itself, increase profit from each additional unit when price, cost per unit, and total fixed costs remain unchanged.

4) Seasonality and capacity utilisation. At full capacity, an additional project may require rush premiums, cause downtime because of coordination difficulties, or require expensive subcontracting. If additional costs and the forgone result from other orders exceed additional revenue, the marginal effect will be negative. With spare capacity, the same project may make a positive contribution; calculate the result for the specific conditions.

Where can you get the figures and build the calculation into your accounting?

The calculation requires consistent data: which costs depend on volume, which are directly attributable to a project, and which are allocated between projects. Direct and variable costs are different classifications: a direct cost can be fixed or variable in relation to the selected volume. For more on allocating project costs, see Direct costs: what to attribute to a project (in Russian).

Record the selling price and costs separately, specifying the unit of measurement, the amount of work, and the recognition period. Identify the variable portion of costs when calculating contribution margin; use full cost to assess whether all expenses are covered. This helps you discuss each project's contribution and the overall operating result with the team.

When choosing a working tool, including the 101 App, decide in advance how you will maintain project data on price, volume, and costs. The calculation requires comparable inputs and verified cost classification rules. Check the specific way of entering those data against the chosen tool's current capabilities.

For regular monitoring, you can assemble a set of measures: contribution margin by project, the contribution margin ratio when revenue is positive, monthly fixed operating costs, the break-even point, and trends by quarter. Compare measures for equivalent periods using consistent accounting rules. For more on profitability, see the article on how to calculate business profitability.