What is Build vs Buy Decision?
The build vs buy decision compares the total cost of developing software in-house against purchasing an existing solution. Building offers full customization and no recurring license fees, while buying provides faster deployment and proven reliability. The right choice depends on how core the functionality is to your competitive advantage. Compare SaaS investment returns with the SaaS ROI Calculator and evaluate vendors with the Vendor Comparison Calculator.
The Formula
Formula
Build Total = Initial Development Cost + (Annual Maintenance ร Years) Buy Total = (Annual License Fee ร Years) + Implementation Cost + Training
Worked Example
Worked example
A company needs a project management tool. Build: $40,000 initial development + $8,000/year maintenance. Buy: $12,000/year license + $5,000 implementation. 5-year comparison.
- 01Build total = $40,000 + ($8,000 ร 5) = $80,000
- 02Buy total = ($12,000 ร 5) + $5,000 = $65,000
- 03Year 1: Build $48,000 vs Buy $17,000
- 04Break-even: Build becomes cheaper at year 8.75
Result
Over 5 years, buying saves $15,000 (19%). Building only becomes cheaper after year 8.75, and that assumes zero scope changes or major refactoring.
Why This Matters
Opportunity cost
Developers building internal tools aren't building your product. If your engineering team is your biggest expense and competitive advantage, every hour spent on non-core tools is an hour not spent on features that drive revenue.
Maintenance burden
Custom software requires ongoing maintenance: bug fixes, security patches, infrastructure updates, and feature requests. This "maintenance tax" of 15-25% of initial build cost per year is often underestimated and grows as the codebase ages.
Time-to-market advantage
Buying a proven solution gets you operational in days or weeks. Building from scratch takes months. In competitive markets, the months spent building infrastructure are months your competitors are acquiring customers and iterating on product.
Common Mistakes
Underestimating build costs by 2-3x
Software projects consistently overrun estimates. A $40,000 estimate typically becomes $80,000-120,000 once edge cases, testing, documentation, and scope changes are included. Always multiply initial estimates by 2-3x for realistic budgeting.
Building commodity features
If the functionality exists in mature SaaS products (CRM, email, project management, analytics), buying is almost always better. Build only when the tool is core to your competitive advantage and no existing solution meets your needs.
Not factoring in hiring risk
Custom builds depend on the developers who built them. If the lead developer leaves, institutional knowledge walks out the door. Rebuilding that context costs 3-6 months of another engineer's time. Purchased solutions have vendor support and documentation that survive team turnover.
Industry Benchmarks
Source: Flexera 2025 State of IT Report