Build vs. Buy Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Build vs. Buy Calculator turns a familiar business question into a compact set of numbers, so you can see the relationship without building a separate spreadsheet.

What this calculator does

Build vs. Buy Calculator compares the modeled total cost of making the required units internally with the total cost of buying them from an outside source. That makes the output useful for the specific relationship being measured here, while keeping any unentered business or investment assumptions outside the calculation.

How to use it

Enter Currency, Units needed, Build option: fixed cost, Build option: variable cost per unit, Buy option: fixed/procurement cost, and Buy option: purchase cost per unit. Use figures from the same reporting period and the same accounting, workforce, inventory, or campaign definition wherever possible. The currency selector changes display currency only; it does not perform an exchange-rate conversion. Before using the result in a decision, recheck unusually large or negative values against the source data rather than assuming the calculator is correcting an inconsistent input.

How the calculation works

Build total = build fixed cost + build variable cost per unit × units needed. Buy total = procurement fixed cost + purchase cost per unit × units needed. Comparing the totals shows which option is cheaper at the entered volume and also makes the fixed-versus-variable-cost tradeoff visible.

Example

For 1,000 units, building costs $12,000 while buying costs $5,000 with the default assumptions. That makes buying cheaper by $7,000 in this scenario.

How to interpret the result

Treat the lower modeled total as the cheaper cost scenario at that exact volume, not as an automatic purchasing decision. Quality, lead time, capacity, maintenance, switching cost, supplier risk, scrap, and the value of internal flexibility can outweigh a small numerical cost advantage.

Limitations and notes

The calculation is only as consistent as its inputs. Accounting policy, attribution rules, period length, one-time items, seasonality, and local reporting conventions can change what should be included in a numerator or denominator. Use the same definitions when comparing periods, and do not treat a simplified ratio as a complete operational diagnosis.