The build or buy decision comes down to three factors: how standard your needs are, how many users you have, and how long you plan to use the software. For most UK SMEs, the answer is not obvious. A SaaS subscription that looks cheap at 10 users can become expensive at 80. Custom software that seems costly upfront can save money over five years. The right choice depends on your specific situation, not on a general rule.
We help UK businesses make this decision with a clear framework. The goal is not to sell you custom software. It is to find the path with the lowest total cost and highest fit for your actual needs. You can start with our SaaS ROI calculator to get a quick cost comparison.
When Should You Buy Off-the-Shelf Software?
Buying is the right choice when your needs are standard and well-served by existing tools. If your accounting, CRM, project management, or communication needs match what the market offers, buying SaaS is faster, cheaper, and lower risk than building.
The advantages of buying include:
- Speed: You can start using the software immediately, with no development time.
- Lower upfront cost: Monthly subscriptions spread the cost, though this becomes a liability at scale.
- Proven features: Established SaaS platforms have been refined by thousands of users.
- Support and updates: The vendor handles maintenance, security patches, and feature updates.
The disadvantages become visible over time. Per-seat pricing scales linearly, so a platform that costs 500 per month at 10 users costs 4,000 per month at 80 users. You are locked into the vendor roadmap, which may not match your needs. Customisation is limited to what the platform allows. And when you want to leave, your data may not be easy to export.
When Should You Build Custom Software?
Building custom software is the right choice when your workflow is genuinely different from what SaaS platforms offer, when you have enough users to justify the upfront cost, or when the software itself gives you a competitive advantage.
The advantages of building include:
- Exact fit: The software does precisely what your business needs, no more and no less.
- No per-seat costs: You own the software, so adding users costs nothing beyond infrastructure.
- Full control: You decide the roadmap, the features, and the integrations.
- Data ownership: Your data lives in systems you control, not in a vendor cloud you cannot fully access.
- No vendor lock-in: You are not dependent on a third party pricing decisions or continued existence.
The trade-off is upfront cost and time. Custom software takes months to build and requires ongoing maintenance. But for businesses with 50 or more users on a SaaS platform, the five-year total cost of custom software is often lower. See our detailed comparison on custom software vs SaaS total cost of ownership.
How Do You Compare the Total Cost?
The honest comparison looks at total cost of ownership over three to five years, not just the first year. SaaS looks cheaper in year one. Custom software looks cheaper by year three or four, depending on your user count.
To compare properly, calculate:
- SaaS total cost: Monthly per-seat cost multiplied by users multiplied by months, plus integration costs, admin overhead, and an allowance for price increases (SaaS prices rise, typically 5 to 10 percent annually per Gartner research on SaaS pricing trends).
- Custom software total cost: Upfront development cost, plus annual maintenance (typically 15 to 20 percent of build cost), plus hosting and infrastructure, plus any internal team time for support.
Use our SaaS ROI calculator to do this comparison with your own numbers. The crossover point, where custom software becomes cheaper, is typically between 30 and 60 users depending on the platform.
What About a Hybrid Approach?
Many UK SMEs benefit from a hybrid approach. Keep SaaS for standard needs like email, accounting, and video conferencing. Build custom software for the processes that differentiate your business or where SaaS costs are spiralling. This gives you the speed of buying where it makes sense and the control of building where it matters.
We often recommend starting with SaaS to validate a process, then moving to custom software when the process is proven and costs justify it. The key is choosing SaaS tools with good data export, so migration is possible. See our guide on choosing a software development partner when you are ready to build.
What Is the Build vs Buy Decision Framework?
A practical framework for the decision:
- Assess fit: How closely do existing tools match your needs? If 80 percent or more, buy. If less than 50 percent, build.
- Calculate TCO: Compare three-year and five-year costs at your current and projected user count.
- Evaluate differentiation: Is the software a commodity or a competitive advantage? Commodities: buy. Advantages: build.
- Consider timing: Do you need it now (buy) or can you wait three to six months (build)?
- Check data portability: If buying, can you export your data? If not, the lock-in cost is significant.
This framework gives you a defensible answer, not a gut feeling. For most UK SMEs with 10 to 250 employees, the decision is clear once the numbers are on the table.