Build vs Buy Calculator - Software Cost Comparison
Compare the total cost of building software in-house versus buying a vendor solution.
Enter upfront and monthly costs for both options plus opportunity cost to see which route is cheaper.
Build vs Buy Calculator - Software Cost Comparison
Compare the total cost of building software in-house versus buying a vendor solution.
About the Build vs Buy Calculator
Build vs Buy Calculator is designed for software sourcing cost comparison, where a small change in one input can alter a decision, budget, or performance story. The calculator keeps the assumptions visible beside the result so the number can be reviewed instead of copied blindly. Use the fields as a compact worksheet: enter the values using the units shown on each label, calculate the primary result, then read the supporting lines to understand which driver is moving the answer.
The calculation adds upfront, monthly, time-horizon, and opportunity costs for the build option and compares them with vendor setup and subscription costs. In plain terms, Build total = build upfront + build monthly x months + opportunity cost; buy total = buy setup + vendor monthly x months. The supporting outputs are included because the headline number rarely gives enough context on its own. Margins, rates, totals, variances, or remaining balances explain whether the result is caused by price, volume, time, cost structure, or exposure.
Common use cases include evaluating SaaS replacements, planning internal platform work, preparing procurement business cases, comparing total cost of ownership, and explaining time-horizon sensitivity. A practical review usually compares at least three cases: conservative, likely, and optimistic. Change one input at a time so the sensitivity is clear; if a small input movement creates a large output change, document the assumption and look for a better source before presenting the result.
Important caveats include implementation risk, security reviews, switching costs, vendor lock-in, roadmap control, maintenance burden, support staffing, and benefits that are strategic rather than purely financial. The calculator is a deterministic planning aid, not a substitute for professional advice, policy review, tax guidance, legal review, HR judgment, brokerage instructions, or a full financial model. Rounding can also matter when the result will be used in contracts, accounting entries, payroll conversations, or regulated decisions.
For best results, keep time periods and units consistent. Enter percentages as ordinary percentage values, such as 8 for 8%, rather than decimals. The recommendation is based on lower modeled cost over the selected months, not on feature fit or delivery risk. After calculating, compare the answer with an independent estimate or source document and save the assumptions that support the scenario.
Build vs Buy Calculator Examples
Use these examples to check the calculation pattern and compare common scenarios.
| Inputs | Output | Notes |
|---|---|---|
| $180,000 build upfront, $12,000/month build, $40,000 opportunity cost, $25,000 setup, $18,000/month buy, 36 months | Build saves $21,000 | Higher upfront build cost is offset by lower monthly run cost. |
| $300,000 build upfront, $20,000/month build, $60,000 opportunity cost, $50,000 setup, $15,000/month buy, 24 months | Buy saves $430,000 | Vendor economics dominate over a shorter horizon. |
| $100,000 build upfront, $8,000/month build, $40,000 opportunity cost, $60,000 setup, $14,000/month buy, 48 months | Build saves $208,000 | Longer horizons favor lower ongoing internal cost. |
How to Use the Build vs Buy Calculator
- Enter each input using the units shown in the field labels.
- Click Calculate to run the formula and show the headline result.
- Review the supporting result cards to understand the drivers behind the answer.
- Change one assumption at a time to compare conservative, likely, and optimistic scenarios.
Build vs Buy Calculator FAQ
What costs belong in the build option?
Include engineering, design, infrastructure, security, maintenance, and implementation costs that would be incurred internally. Opportunity cost should reflect the value of delaying other work with the same team.
What costs belong in the buy option?
Include vendor setup, subscription, implementation services, integrations, support tiers, and required add-ons. If the vendor charges usage-based fees, convert the expected usage into a monthly estimate.
Why does the time horizon matter so much?
Build options often have high upfront cost and lower ongoing cost, while buy options often have lower entry cost and higher recurring fees. A longer horizon can reverse the recommendation.
Does the calculator decide product fit?
No. The result compares modeled cost only. Feature coverage, compliance, support quality, vendor risk, and strategic control should be reviewed separately.
How should opportunity cost be estimated?
Use a realistic value for delayed roadmap items, lost revenue, or engineering capacity diverted from other priorities. If the estimate is uncertain, run low and high cases to see whether the recommendation changes.