Build vs Buy: When to Build Custom Software
Buy commodity software. Build your core differentiator. If a competitor can sign up for the same tool you’re evaluating, that tool cannot be your competitive moat. The real decision is: does this software encode something unique about how your business operates? If yes, build it. If no, buy it and move on.
That said, “buy” and “build” each carry hidden costs that rarely appear in the comparison spreadsheets I see founders share with me. I’ve watched teams get burned by both: a $50K Salesforce implementation that nobody used, and a $300K custom CRM that shipped 14 months late and still didn’t cover half the features Salesforce gave them on day one. The framework below is what I use with every startup I advise.
Why the Build vs Buy Decision Gets It Wrong So Often
According to Gartner’s 2024 Tech Trends survey of more than 3,400 respondents across nine countries, 68% of fast-growing businesses regret a software purchase. That’s not a data quality problem. That’s a decision-making process problem.
Most teams frame the choice as: “subscription cost vs. estimated build cost.” That framing misses about half of the real numbers on both sides. When I sit down with a founder to work through this, I’m looking at four cost buckets, not two.
The Real Cost Model: Four Buckets on Each Side
Buying SaaS: What the Sticker Price Hides
The subscription fee is the smallest line item in the true SaaS total cost of ownership.
Research from CloudNuro’s SaaS TCO analysis puts it plainly: the headline subscription price represents only 25-40% of actual three-year TCO. The rest is integration engineering, data migration, onboarding and training time, internal support overhead, and the price increases that come at renewal.
On that last point: Vertice’s SaaS Inflation Index, which tracks actual contract renewals across thousands of vendors, found that SaaS prices rose 12.2% in 2024, compared to 2.7% general inflation. That’s a 4.5x gap. You sign at one price, and within three years you’re paying materially more for the same product.
The lock-in risk is not theoretical. When Broadcom acquired VMware, perpetual licenses were eliminated and some customers faced price increases exceeding 1,000%. One vendor decision, made years before you were a customer, can restructure your cost base overnight.
And then there’s waste. The Zylo 2024 SaaS Management Index, which tracks over 30 million licenses representing $34 billion in SaaS spend, found that the average organization uses only 49% of provisioned licenses. That translates to $18 million per year in wasted SaaS spend at the average enterprise. Startups waste proportionally less in absolute dollars but often proportionally more as a share of runway.
Building Custom: What the Dev Quote Hides
Build quotes suffer from a different set of blindspots.
The most common error is treating the initial build cost as the total cost. It isn’t. According to Vention Teams’ 2024 Software Maintenance Costs Benchmark Report, annual software maintenance runs 15-25% of the original development budget every year. A $200,000 custom build costs $30,000-$50,000 per year to maintain before a single new feature is added. Over five years, that’s the equivalent of building the software twice.
Developer salaries compound this. The U.S. Bureau of Labor Statistics reports the median annual wage for software developers at $133,080 as of May 2024. Every engineer you hire to build and maintain custom software carries that cost plus benefits, tooling, and management overhead.
And scope creep is statistically inevitable. A McKinsey study of more than 5,000 large IT projects found that the average large IT project runs 45% over budget. Seventeen percent of those projects produced overruns so severe (200-400%) that they threatened the company’s viability. This isn’t because developers are incompetent. It’s because requirements change, integration is harder than it looks, and founders underestimate edge cases.
The Decision Framework: Four Questions That Settle It
I use these four questions in order. The first “buy” answer typically ends the analysis.
1. Is this software part of what makes you different?
If the answer is no, buy it. Email infrastructure, payments, scheduling, document signing, video calls: your competitors use the same tools. The tool is not your moat.
If the answer is yes, move to question 2.
2. Can you describe the requirement precisely enough to build it?
Vague differentiators don’t survive translation into working software. “Our matching algorithm is smarter than theirs” needs to become: a defined input schema, explicit matching rules, measurable output quality criteria, and a way to improve it over time. If you can’t write that spec, you’re not ready to build. Buying gives you working software while you sharpen the requirement.
3. What happens if the vendor changes price, gets acquired, or shuts down?
For nice-to-have tooling, the answer is: “we find another vendor.” For anything in a critical path, vendor dependency becomes existential risk. If the honest answer is “we would be seriously disrupted,” that’s a signal to either build or establish a contractual data portability guarantee before you buy.
4. What is the three-year total cost on each side?
Run the numbers with the full cost model. Include integration and migration on the buy side. Include maintenance and staffing on the build side. Apply a 12% annual price increase assumption to SaaS renewals. The result is often closer than the initial gut reaction suggests, which is why gut reactions aren’t good enough.
The Third Path: Buy the Platform, Build the Layer
This is the approach I recommend most often for startups, and it’s the one that appears least often in the build vs buy framing.
Most SaaS products cover 80% of a use case well. The remaining 20% is where your differentiation lives. Rather than building the full 100% from scratch or compromising on the 20% with a vendor’s workaround, you can:
- Buy a platform that covers the commodity 80% (scheduling, CRM, data pipeline, payments)
- Build a lightweight custom layer on top that encodes your unique process or algorithm
- Own the custom layer as IP; treat the platform as infrastructure
This is how I’ve helped founders avoid both the $300K custom CRM mistake and the $50K Salesforce regret. A $15K custom integration layer on top of an off-the-shelf CRM often delivers more competitive value than either extreme.
This approach is exactly what I describe in more detail in the MVP development for startups guide: ship the smallest thing that creates real value, then build custom only where value is provably differentiated.
Build vs Buy Comparison Table
| Factor | Buy (SaaS) | Build (Custom) | Buy + Build Layer |
|---|---|---|---|
| Time to first value | Days to weeks | Months | Weeks to months |
| Upfront cost | Low | High | Medium |
| True 3-year TCO | 2.5x-5x sticker | 2x-3x build quote | Medium-low |
| Vendor lock-in risk | High | None | Low |
| Maintenance burden | Vendor-managed | 15-25%/yr of build cost | Low (layer only) |
| Competitive differentiation | None | High (if scoped right) | Medium-high |
| Execution risk | Low | High (45% budget overrun avg) | Low-medium |
Frequently Asked Questions
When should a company build custom software instead of buying SaaS?
Build custom software when it encodes a process, algorithm, or workflow that is genuinely unique to your business and cannot be replicated by a competitor buying the same vendor product. If the software is part of your value proposition to customers, or if the 20% gap between what a vendor offers and what you need is the exact 20% that matters competitively, custom development is justified. Everything else should be bought.
What is the total cost of ownership of SaaS vs custom software?
SaaS TCO is typically 3-5x the headline subscription price over three years, once you account for integration, migration, training, internal support, and annual price increases averaging 12.2% in 2024. Custom software TCO includes the initial build cost plus 15-25% of that cost every year in maintenance. Both numbers tend to surprise teams who only looked at the quoted price.
How much does it cost to build custom software vs buying an off-the-shelf solution?
This depends entirely on scope, but the pattern I see consistently is: buying costs less initially and more over time (especially after lock-in), while building costs more initially and compounds if scope grows. For a startup, a $50K-$150K custom build often competes with a $10K-$30K/year SaaS contract. Over five years with maintenance, they can be within the same order of magnitude. The real question is whether the custom build delivers differentiated value the SaaS cannot.
What are the hidden costs of SaaS subscriptions?
Integration engineering, data migration from previous systems, user training and change management, internal support overhead when the tool breaks or changes, annual price increases (averaging 12.2% in 2024 according to Vertice), and seat underutilization (the average company uses only 49% of provisioned licenses). The subscription line item is typically only 25-40% of your actual three-year spend.
What is vendor lock-in and how do you avoid it?
Vendor lock-in is when switching away from a vendor becomes prohibitively expensive due to data formats, integrations, or contractual terms. The VMware/Broadcom situation is the extreme example: prices increased over 1,000% because customers had no practical path to switch. To avoid it: negotiate data export rights in your contract before signing, prefer vendors with open data formats and public APIs, and treat any SaaS that becomes a critical path dependency as a build candidate for your next planning cycle.
How do you calculate build vs buy ROI?
Build a three-year model with these inputs: SaaS side includes license fees with 12% annual escalation, integration cost, migration cost, training cost, and estimated internal support hours. Build side includes development cost, annual maintenance at 20% of build cost, hosting and infrastructure, and a 45% contingency buffer for overruns. Compare total costs and weight by execution risk. Then ask separately whether the custom build delivers revenue or retention impact the SaaS cannot. If yes, how much? That number often changes the analysis more than any cost line.
What software should companies always buy rather than build?
Authentication and identity (Auth0, Clerk), payments (Stripe), email infrastructure (Resend, Postmark), video conferencing, document signing, general CRM, analytics, and monitoring. These are solved problems with well-funded vendors. Building your own auth or payments infrastructure is a security liability. Building your own analytics tool is a distraction. The engineering time saved goes toward building what only you can build.
The Short Version
Buy anything a competitor can also buy. Build only what encodes your unique process or IP. Account for the full cost model on both sides: SaaS sticker price is not TCO, and the build quote is not the lifetime cost. When in doubt, use the third path: buy the commodity platform, build the differentiated layer on top, own the layer as IP.
If you’re working through this decision right now and want a second opinion from someone who has done it across a dozen startups, I offer a free 30-minute consultation at sparkable.dev/consult. No pitch. I’ll tell you what I actually think, including if the answer is “just buy it.”