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Step Fixed Costs: Recheck Break-Even at Each Level

Model costs that jump when capacity expands and test whether each calculated break-even point fits the range that produced it.

By PriceAndProfit Editorial Updated 3 min read

On this page
  1. Worked calculation
  2. Decision checks and limits
  3. Apply the calculation

Some fixed costs remain constant only within an activity band. Another shift, supervisor, warehouse area, or machine lease can create a step increase when volume crosses a threshold. A single fixed-cost amount then fails to describe the entire business. Calculate each range separately and accept a break-even result only if it lies inside the range where that cost amount applies.

Operating profit moves from $2,000 at 500 units to negative $2,980 at 501 when the fixed-cost tier changes.
Hypothetical monthly capacity tiers. Profit returns to zero at 650 units under the higher fixed-cost level.

Worked calculation

Operating profit within a band = units × that band’s unit contribution − that band’s fixed costs; accept break-even only within the band’s feasible unit range

Assume a business earns $20 contribution per unit. Fixed costs are $8,000 for monthly volume from zero through 500 units. For 501 through 1,000 units, an additional capacity commitment raises fixed costs to $13,000. In the first range, break-even is $8,000 divided by $20, or 400 units, which is feasible within that band. In the second range, break-even is $13,000 divided by $20, or 650 units, also within its band.

This model can have more than one break-even crossing. At 500 units, contribution is $10,000 and operating profit is $2,000. At 501 units, contribution rises to $10,020 but fixed costs jump to $13,000, creating a $2,980 loss. Profit reaches zero again at 650 units. Reporting only the first 400-unit break-even point would conceal the loss that appears when the next capacity commitment begins.

Hypothetical worked example
Monthly unitsApplicable fixed costContributionOperating profit
400 $8,000 $8,000 $0
500 $8,000 $10,000 $2,000
501 $13,000 $10,020 −$2,980
650 $13,000 $13,000 $0

Decision checks and limits

Check whether the step is truly automatic at the stated quantity. If the business can decline extra demand and remain at 500 units, the 501-unit outcome is a decision scenario, not an unavoidable consequence of receiving one more inquiry. If the additional facility is committed for a full year, its cost may persist during later low-volume months rather than immediately dropping back to the lower range. The worksheet must reflect actual commitment timing.

An algebraic result outside its band is invalid for that band's equation. If fixed costs in the upper range were $22,000, dividing by $20 would suggest 1,100 units, beyond the 1,000-unit capacity assumed there. That range has no break-even solution. Show the maximum contribution and resulting loss instead of extending the line beyond its operating conditions. Price changes, overtime, and additional variable costs at higher volume can require a different contribution amount for each band as well.

Apply the calculation

  1. Map the actual commitments

    Record thresholds, capacity limits, and the duration of each added cost before calculating any volume target.

  2. Solve and validate each band

    Divide that band's fixed cost by its contribution, then reject results outside the allowed quantity range.

  3. Compare choices around the step

    Calculate profit just below and above the threshold, including whether the extra capacity can be delayed, avoided, or used for other work.

Method references: OpenStax: Cost behavior patterns. Accessed October 22, 2026. All dollar figures are hypothetical worked examples.

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