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Methodology

Contribution Margin Planner methodology

Reconcile unit contribution with period fixed-cost coverage.
Duc Nguyen X.By Duc Nguyen X.· Founder, Margin101Last reviewed: View update historyMethodology

Educational only: Business decision support, not accounting, tax or legal advice.

Privacy: Calculations run locally; Margin101 does not receive your commercial inputs.

Update policy: Reviewed when formulas or official dependencies change.

Scope: Market-neutral small-business planning using your own assumptions.

1. Formulas and units

Total Contribution Ex Tax
totalContributionExTax = unit contribution × units

Where

units
Units (whole product units/comparison period)Source: User assumption
totalContributionExTax
Total Contribution Ex Tax (currency units, ex tax)Source: Calculated output
contributionPerUnitExTax
Contribution Per Unit Ex Tax (currency units, ex tax)Source: Calculated output
Contribution Per Unit Ex Tax
contributionPerUnitExTax = unit price − unit variable cost

Where

unitPriceExTax
Unit price (currency units/product unit, ex tax)Source: Business record
unitVariableCostExTax
Variable cost per unit (currency units/product unit, ex tax)Source: Business record
totalContributionExTax
Total Contribution Ex Tax (currency units, ex tax)Source: Calculated output
contributionPerUnitExTax
Contribution Per Unit Ex Tax (currency units, ex tax)Source: Calculated output
Contribution Ratio
contributionRatio = unit contribution ÷ unit price

Where

unitPriceExTax
Unit price (currency units/product unit, ex tax)Source: Business record
totalContributionExTax
Total Contribution Ex Tax (currency units, ex tax)Source: Calculated output
contributionPerUnitExTax
Contribution Per Unit Ex Tax (currency units, ex tax)Source: Calculated output
contributionRatio
Contribution Ratio (currency units, ex tax)Source: Calculated output
Break Even Units
breakEvenUnits = ceil(fixed costs ÷ positive unit contribution)

Where

fixedCostsExTax
Fixed costs (currency units/comparison period, ex tax)Source: Business record
totalContributionExTax
Total Contribution Ex Tax (currency units, ex tax)Source: Calculated output
contributionPerUnitExTax
Contribution Per Unit Ex Tax (currency units, ex tax)Source: Calculated output
breakEvenUnits
Break Even Units (operational units)Source: Calculated output
Fixed Cost Coverage Ex Tax
fixedCostCoverageExTax = total contribution − fixed costs

Where

fixedCostsExTax
Fixed costs (currency units/comparison period, ex tax)Source: Business record
totalContributionExTax
Total Contribution Ex Tax (currency units, ex tax)Source: Calculated output
contributionPerUnitExTax
Contribution Per Unit Ex Tax (currency units, ex tax)Source: Calculated output
fixedCostCoverageExTax
Fixed Cost Coverage Ex Tax (currency units, ex tax)Source: Calculated output

Money inputs and outputs use the currency selected in the scenario without changing the canonical methodology. Rates, margins, utilisation and buffers are entered as percentages and converted to decimal values for calculation.

2. Worked example

Input assumptions

The worked rows below come directly from the registered engine and visible default fixture.

Calculation and outputs

Example

The worked rows below come directly from the registered engine and visible default fixture.

Total Contribution Ex Tax
20,000 currency units
Contribution Per Unit Ex Tax
40 currency units
Contribution Ratio
0.47 currency units
Break Even Units
300
Fixed Cost Coverage Ex Tax
8,000 currency units

The exact engine-derived outputs are shown in the labelled rows below.

Interpretation

Period contribution is the amount available to cover fixed costs and profit after the entered variable costs.

3. Validation and boundary checks

  • All inputs must be finite and within the visible validation boundaries.
  • Rates use decimal values below 100%; whole-unit thresholds round upward only where the engine names that rule.
  • All compared monetary inputs use one consistent ex-tax basis and planning period.

4. Assumptions and source classification

  • Every cost, price, fee and volume is supplied by the user; no market benchmark is inferred.
  • Indirect tax is excluded from retained commercial economics unless a dedicated input explicitly models it.
  • The engine retains full precision and display formatting never feeds back into calculation.

This planner has no current policy-data dependency. Its commercial assumptions are user supplied. Registered family-level regression suites exercise the shared business-logic engine and worked-result reconciliation.

5. Limitations

  • The model does not forecast demand, competitor response, supplier negotiation outcomes or capacity.
  • It does not replace accounting, tax, legal or financial advice.

This is educational decision support, not tax, accounting, legal or financial advice. Check the treatment of your actual transactions under the rules that apply to your business and seek qualified advice where appropriate.

6. Update and evidence policy

Registered family-level suites test formula invariants and example reconciliation; the release ledger records that coverage without claiming a separate oracle for every line of public copy. There is no official threshold or benchmark to refresh for this planner. Commercial inputs remain user-supplied because they vary by business and contract.

Change history

  1. : Initial public release of the planner and methodology after pre-launch calculation, content, source and interaction review.

Related reading

Guides to interpret the decision and its assumptions.

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