Build vs Buy Decision Analyzer

Formula

TCO = InitialCost + (AnnualCost × Years)

We sum the initial CapEx (Development or Implementation fees) and the recurring OpEx (Maintenance or Subscription fees) over the selected time horizon to find the true cost.

Worked Examples

Example 1: Internal Tool Over a Three-Year Horizon

Problem:Building costs $50,000 up front plus $10,000 a year to maintain. Buying costs $5,000 to implement plus a $15,000 annual subscription. Over three years, which is cheaper - and when does that flip?

Solution:TCO = InitialCost + (AnnualCost x Years) Build: $50,000 + ($10,000 x 3) = $50,000 + $30,000 = $80,000 Buy: $5,000 + ($15,000 x 3) = $5,000 + $45,000 = $50,000 Buy is cheaper by $30,000 over three years. But find the crossover before deciding. Set the two equal and solve for the number of years n: 50,000 + 10,000n = 5,000 + 15,000n 45,000 = 5,000n n = 9 years Check at year 9: Build = $50,000 + $90,000 = $140,000; Buy = $5,000 + $135,000 = $140,000. Identical. So buying wins for any horizon shorter than nine years, and building only pays back if the tool is still in service after that. For an internal utility tool, nine years is far beyond the point at which requirements will have changed - buy.

Result:Buy saves $30,000 over three years. Break-even is year 9, well past the useful life of most internal tools.

Example 2: Core Product Capability Over Five Years

Problem:A capability central to the product costs $100,000 to build plus $20,000 a year to maintain, or $50,000 to implement plus $50,000 a year to license. Over a five-year horizon, which wins?

Solution:Build: $100,000 + ($20,000 x 5) = $100,000 + $100,000 = $200,000 Buy: $50,000 + ($50,000 x 5) = $50,000 + $250,000 = $300,000 Build is cheaper by $100,000. Crossover: 100,000 + 20,000n = 50,000 + 50,000n 50,000 = 30,000n n = 1.67 years Building overtakes buying after roughly 20 months - inside the first two years. That is the signature of a core capability: high recurring vendor cost against modest maintenance, because the vendor is charging for something central to your value rather than for undifferentiated plumbing. The rule of thumb this supports: buy what is undifferentiated and build what is differentiating. A payroll system is undifferentiated no matter how large you are; the thing customers actually pay you for is not.

Result:Build saves $100,000 over five years, and overtakes buying after just 1.67 years.

Example 3: The Costs TCO Leaves Out

Problem:The three-year internal tool comparison said buy, saving $30,000. What does that arithmetic ignore, and when is it wrong enough to change the answer?

Solution:Missing on the build side: Opportunity cost. If two engineers spend four months on it and the fully loaded cost is $200,000 per engineer per year, that is 2 x $200,000 x (4/12) = $133,333 of engineering capacity - which may already exceed the $50,000 build estimate, and it is capacity not spent on the roadmap. Maintenance drift. The $10,000 annual figure rarely survives contact with dependency upgrades, security patches and the departure of whoever wrote it. Missing on the buy side: Price escalation. A subscription rising 7% a year turns $15,000 into $15,000 x 1.07^2 = $17,174 by year three. The three years then bill $15,000 + $16,050 + $17,174 = $48,224, so the true buy cost is $53,224 rather than $50,000. Switching cost. Data migration and retraining are paid at exit, not at purchase. I

Result:A $30,000 three-year gap is within estimation error once opportunity cost and 7% price escalation are added. Only act on large, durable gaps.

Frequently Asked Questions

What are hidden costs of Building?

Maintenance, hosting, security patching, tech debt, and opportunity cost (your engineers aren't working on core product). Maintenance is typically 20% of build cost annually.

What are hidden costs of Buying?

Integration costs, training, lack of customization, price hikes by the vendor, and data lock-in.

When should I Build?

When the capability is a core competitive advantage (your 'Secret Sauce'), or when no vendor meets your specific regulatory/functional needs.

When should I Buy?

For commodity functions (Email, CRM, HR, Payroll). Why reinvent the wheel when Salesforce or Stripe exists?

What is Opportunity Cost?

The value of the next best alternative. If your engineers spend 3 months building a CRM, they aren't building customer-facing features that generate revenue.

Does this include Time to Value?

The calculator focuses on cost. But remember: Buying is usually instant. Building takes months. Delay has a cost.

What about Intellectual Property (IP)?

Building creates IP (Asset). Buying is an Expense. Investors generally prefer you own your core tech but rent your back office.

How long is the horizon?

Software typically has a useful life of 3-5 years before needing a major rewrite. 3 years is a standard comparison period.

Is 'Low-Code' a compromise?

Yes. Low-code/No-code tools offer a middle ground: faster/cheaper than custom code, more flexible than rigid SaaS.

What about Exit Strategy?

If you Buy, ensure you can export your data. If you Build, ensure you document code so future hires can maintain it.

Background & Theory

The Core Decision Framework

The decision isn't just financial. It's strategic.

Core: Your unique differentiator. BUILD.
Context: Necessary but not unique (e.g., email). BUY.

Total Cost of Ownership (TCO)

Most people compare License Fees vs Developer Salaries. They miss:

Build: QA, DevOps, Hosting, Security Audits, Documentation, Onboarding new devs.
Buy: Vendor management, Legal review, Procurement cycles, Integration maintenance.

Strategic Tips

Start with Buy: Prove the value. If you outgrow the vendor, *then* Build.
Hybrid: Buy the engine (e.g., Stripe), Build the UI (Checkout form).

History

The Mainframe Era

In the 1960s-80s, you built everything. There was no software market. If you wanted payroll, you wrote COBOL.

The Package Software Era

In the 1990s, COTS (Commercial Off-The-Shelf) software emerged. Companies bought CDs of SAP or Oracle. Implementation took years and millions, but it was still cheaper than building an ERP from scratch.

The SaaS Revolution

Salesforce (1999) proved software could be rented. The "No Software" motto shifted the default from Build to Buy. Today, the API economy means we glue together SaaS blocks rather than writing monoliths.

Common Misconceptions

Myth: Building is free because we have engineers. Reality: Engineer time is the most expensive resource you have.
Myth: Buying is inflexible. Reality: Modern SaaS with APIs and Webhooks is highly extensible.