Custom software vs SaaS:
when to build and when to buy.
Short answer: Buy SaaS when your needs are standard and the tool is affordable. Build custom when your business logic is unique, your SaaS bill is spiralling, or data control matters. Most businesses should do both — SaaS for generic functions, custom for competitive-edge workflows.
Custom software vs SaaS — compared
| Criteria | Custom Software | SaaS / Off-the-shelf |
|---|---|---|
| Upfront cost | £10,000–£70,000+ | Low (often free trial or £30–£500/month) |
| Ongoing cost | Low — hosting + maintenance only | Compounding — per-seat, per-feature pricing grows with team |
| Total cost of ownership (3yr) | Often cheaper for growing teams | Can spiral to £50,000+ over 3 years |
| Customisation | Unlimited — built for your exact workflow | Limited to vendor's roadmap |
| Integration depth | Full control — any API, any data flow | Depends on vendor's integration list |
| Data ownership | You own it — your servers, your control | Vendor servers — GDPR/export considerations apply |
| Time to deploy | 6–20 weeks build time | Days to weeks |
| Vendor risk | None — you own the code | Price hikes, sunsets, acquisitions |
| Competitive edge | High — competitors can't buy the same thing | None — competitors use the identical tool |
When each option wins
Build custom software when…
- Your business logic is genuinely unique to your industry
- You're spending £500–£1,000/month or more on SaaS tools
- Your team wastes time on workarounds for tool limitations
- You need to integrate multiple systems that don't talk to each other
- Data sovereignty or GDPR control is a client requirement
- The software could be productised and sold to others
- You want to hire without paying per-seat fees as you scale
Use SaaS when…
- Your needs are generic and well-served by existing tools
- You need to move fast and budgets are tight
- The tool is a commodity (email, payroll, accounting, calendar)
- You can adapt your workflow to the tool without friction
- The vendor's roadmap aligns with where your business is going
- You don't have the technical capacity to maintain custom software
The 3-year cost comparison
Custom software looks expensive upfront. Over 3 years, the picture changes.
SaaS × 3 years
A growing team of 10 paying £200/user/month = £24,000/year. Add a second tool at £100/user = £12,000/year. After 3 years: £108,000. And you still pay next year.
Custom × 3 years
Build cost: £25,000. Annual hosting + maintenance: ~£3,000/year. After 3 years: £34,000 — regardless of team size. No per-seat fees, ever.
The crossover point
For most UK SMEs spending £500–£1,000/month on SaaS tools, custom software breaks even at 12–18 months. After that, it's pure saving — while retaining full control.
Common questions
Should I build custom software or use SaaS?
Buy SaaS when your needs are standard and affordable. Build custom when your business logic is unique, your SaaS bill is growing, or data control is critical. Most businesses benefit from a hybrid approach.
Is custom software too expensive for an SME?
Not necessarily. A focused custom tool starts from £10,000. If it replaces £800/month in SaaS subscriptions, it pays for itself in 13 months — and saves money every month after that.
What are the biggest risks of building custom software?
Wrong development partner, underspecified requirements, and overbuilding. These risks are mitigated by fixed-scope contracts, iterative delivery (you see progress early), and working with an experienced team.
Can custom software integrate with my existing SaaS tools?
Yes — almost always. Most SaaS tools expose APIs. Custom software can integrate via REST/GraphQL APIs, webhooks or direct database access where available. This is one of custom software's strongest arguments.
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