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Marginal Cost Calculator

Enter your costs and quantities to find the marginal cost per unit.

How it is calculated

Marginal cost compares two production levels: MC = (cost2 − cost1) ÷ (qty2 − qty1). Cost1 and qty1 are the total cost and the output at the first level, cost2 and qty2 the same at the second level. Costs are total costs (fixed plus variable) for the whole run, not per unit, and quantities are units produced. The tool also shows the change in total cost and the change in quantity. Because only differences are used, fixed costs that stay the same cancel out. If the two quantities are equal, nothing can be divided and no result is given. The answer is the average extra cost per unit between the two points, not the exact cost of one single extra unit.

Worked example

A workshop produces 1,000 units at a total cost of 12,500, and 1,200 units at a total cost of 14,150. The change in cost is 14,150 − 12,500 = $1,650.00 and the change in quantity is 1,200 − 1,000 = 200 units. The marginal cost is 1,650 ÷ 200 = $8.25 per unit. The average cost at 1,000 units was 12.50, so each extra unit costs less than the average here, which is why the average cost is still falling.

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Common mistakes

  • Entering cost per unit instead of total cost: both cost fields are total costs for that output level, so unit costs would give a meaningless result.
  • Dividing by the new quantity instead of the change in quantity: 1,650 ÷ 1,200 is not the marginal cost, the divisor is 200.
  • Comparing levels that are far apart: if a new machine or shift was added in between, the result is an average over a jump in fixed costs, not a clean marginal cost.
  • Confusing marginal cost with average cost: average cost is total cost ÷ quantity, and the two are equal only at the lowest point of the average cost curve.

Sources

About this calculator

Marginal cost is the additional cost of producing one more unit of output, calculated as MC = ΔTotal Cost ÷ ΔQuantity — the change in total cost divided by the change in quantity produced. If increasing output from 100 to 101 units raises total cost from $5,000 to $5,045, the marginal cost of that unit is $45, reflecting mostly variable costs like materials and labor since fixed costs (rent, equipment) don't change with output in the short run.

Marginal cost is central to microeconomic theory: a profit-maximizing firm in a competitive market produces up to the point where marginal cost equals marginal revenue (price), and the shape of the marginal cost curve — typically U-shaped due to diminishing returns followed by rising input costs — explains why costs per unit eventually rise as a factory nears capacity. Economics students, manufacturing cost analysts, and pricing managers use marginal cost to decide whether producing additional units is still profitable at the current price.

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Comments (1)

  • Editorial team

    A practical use is a one-off special order. Enter your current output and total cost as the first level, then the output and total cost including the order as the second, and compare the result with the price per unit the customer offers. If the price is below that figure, the order loses money on its own terms. A drop in output is accepted too, so you can price a cutback. Which decision are you using marginal cost for?

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