Growing businesses in the UK and USA spend an average of £3,200–£8,500 per employee per year on SaaS subscriptions. For a 25-person company, that is £80,000–£212,000 every year — and the figure climbs as headcount, integrations, and premium add-ons stack up. Meanwhile, custom software projects that looked expensive at £60,000–£120,000 upfront often cost less than three years of the SaaS tools they replace.
The SaaS vs custom software decision is one of the most consequential technology choices a business leader makes — and it is consistently made with incomplete information. This guide fixes that. You will find a real total cost of ownership framework, worked calculations with realistic numbers, and a decision process built around your actual situation rather than vendor marketing.
The Core Problem: How Businesses Miscalculate SaaS Cost
When businesses evaluate SaaS tools, they typically look at the headline subscription price and stop there. This produces a systematic underestimate of real cost. The full SaaS cost picture includes:
- Base subscription fees: The visible monthly or annual cost — almost always calculated per user, which compounds as the company grows
- Premium feature add-ons: The features you actually need are frequently gated behind higher tiers. The "Starter" plan that looks affordable rarely includes the reporting, API access, SSO, or automation features that make a tool genuinely useful for a growing business
- Integration costs: Connecting multiple SaaS tools requires either expensive native integrations, third-party automation platforms (Zapier, Make) at £20–£200/month each, or custom API work
- Implementation and onboarding: Getting a complex SaaS tool properly configured and staff trained typically costs 1–3 months of someone's time — a real cost that never appears in ROI calculations
- Annual price increases: Most SaaS vendors increase prices 5–15% per year. A tool costing £500/month today costs £900–£1,200/month in five years under typical SaaS pricing trajectories
- Switching costs: When you eventually leave a SaaS platform (and most businesses eventually do), migrating your data, rebuilding integrations, and retraining staff adds £5,000–£50,000 in transition cost
- Workaround labour: When SaaS tools do not fit your processes, people develop manual workarounds — spreadsheets, copy-pasting between systems, manual reconciliation. This invisible labour cost is rarely captured but is often the largest hidden cost of a poor-fit SaaS tool
Total Cost of Ownership: The Right Calculation Framework
A proper TCO comparison must look at the same time horizon for both options — typically 3 years or 5 years. Here is the framework:
SaaS TCO over 5 years
Year 1 cost = (Subscription price × 12) + implementation time cost + integration setup cost + training cost
Year 2-5 cost = (Subscription price × 1.08 annual increase × 12) + ongoing integration maintenance + workaround labour
End-of-period cost = Potential switching/migration cost if you change platforms
Custom software TCO over 5 years
Year 1 cost = Development build cost + deployment/infrastructure setup
Year 2-5 cost = Hosting cost + maintenance retainer (typically 15–20% of build cost per year) + feature development requests
End-of-period benefit = You own the software; no switching cost; can sell, license, or white-label it
TCO Calculator: Three Worked Examples
Example 1: Small Professional Services Firm (12 staff)
A UK consulting firm using HubSpot Professional (£1,035/month), Asana Business (£552/month), Xero Standard (£47/month), Slack Pro (£132/month), and DocuSign Business Pro (£120/month) for a combined £1,886/month or £22,632/year.
Pain points: data does not flow between HubSpot and Asana without Zapier (£99/month extra). Reporting requires manual exports to spreadsheets. The CRM does not track project profitability — they need a separate spreadsheet for that.
| Cost Type | SaaS (5 years) | Custom Platform (5 years) |
|---|---|---|
| Software subscription / build | £127,000 (with 8%/yr increase) | £75,000 (build) |
| Integration tools (Zapier etc.) | £7,200 | £0 (built-in) |
| Manual workaround labour | £18,000 (estimated 3h/week × 5yr) | £2,000 (minimal) |
| Hosting / infrastructure | £0 (included in SaaS) | £9,000 (£150/month × 5yr) |
| Maintenance retainer | £0 | £56,250 (15% of build/yr × 5yr) |
| 5-Year Total | £152,200 | £142,250 |
Verdict: Custom software breaks even by year 4 and costs less over 5 years — while eliminating the workflow friction that currently costs 3 hours of staff time weekly. The productivity gain from a properly integrated system makes the real ROI significantly higher than the numbers suggest.
Example 2: E-commerce Business (8 staff, £2m annual revenue)
A UK retailer using Shopify Advanced (£299/month), Klaviyo (£400/month), Gorgias (£120/month), ShipStation (£89/month), and Brightpearl ERP (£850/month) — totalling £1,758/month or £21,096/year.
Pain points: Brightpearl integration with Shopify requires a £350/month connector. Returns processing is mostly manual. Inventory reporting requires pulling from three systems.
| Cost Type | SaaS (5 years) | Custom Build (5 years) |
|---|---|---|
| Software subscription / build | £119,000 | £95,000 |
| Shopify transaction fees (0.5%) | £50,000 | £0 |
| Integration connectors | £21,000 | £0 |
| Manual ops labour | £25,000 | £5,000 |
| Hosting / maintenance | £0 | £78,750 |
| 5-Year Total | £215,000 | £178,750 |
Verdict: Custom wins clearly — primarily because Shopify's transaction fees and the Brightpearl connector add £71,000 over five years that simply do not exist in a custom build.
Example 3: Early-Stage Startup (4 staff, pre-revenue)
A startup using a collection of free/low-cost SaaS tools: Notion (free), HubSpot Free, Slack Free, Google Workspace Business Starter (£6/user/month). Total SaaS cost: £288/year.
| SaaS | Custom Software | |
|---|---|---|
| Year 1 cost | £288 | £40,000–£80,000 |
| Verdict | SaaS wins by a massive margin at this stage. No startup at 4 people with no revenue should be building custom software. | |
The key lesson from these three examples: custom software almost never wins for small early-stage businesses on cost grounds alone. It starts making financial sense at 15–25 staff, with established revenue, and when the SaaS stack has grown to £1,500–£3,000/month or more.
Beyond Cost: The Non-Financial Factors That Change the Decision
The TCO calculation above assumes your SaaS tools adequately serve your needs. When they do not, the non-financial factors often matter more than the numbers:
Competitive differentiation
When your competitive advantage comes from how you do something — a unique service delivery model, a proprietary methodology, a workflow that competitors cannot easily replicate — SaaS tools force you to operate within their generic model. Every customisation is a workaround. Custom software lets your operational IP live in the product, not in spreadsheets layered over a tool designed for someone else's business. This is the strongest non-financial argument for custom software, and it is often decisive for businesses in specialist markets.
Data ownership and security
Every SaaS tool holds a portion of your business data on its infrastructure. For most businesses, this is an acceptable trade-off. For businesses in regulated industries — legal, financial services, healthcare, defence supply chains — data residency, sovereignty, and security requirements may rule out commercial SaaS platforms entirely. Custom software on private or dedicated cloud infrastructure gives complete control over where data sits, who can access it, and how it is handled under UK GDPR or US CCPA.
Integration depth
The promise of SaaS is that tools integrate with each other. The reality in 2026 is that most business SaaS stacks have 8–15 tools with shallow integrations — data that does not sync in real time, fields that do not map correctly, and automation logic that requires workarounds. When your growth depends on data flowing accurately and instantly between systems, shallow integrations become a genuine operational constraint. Custom software with a unified data model eliminates this entirely.
Vendor risk
SaaS vendors get acquired, pivot their product direction, discontinue features, or raise prices aggressively. Businesses that built their operations on platforms like Mailchimp, Basecamp, or Intercom have experienced significant disruption when the product changed in ways that broke their workflows. Custom software you own cannot be discontinued, price-hiked, or changed without your consent.
When SaaS Is Clearly the Right Choice
- You have fewer than 15 employees and your revenue is under £500,000/year
- Your processes are largely the same as other businesses in your sector — a generic tool fits well
- You need to be live and operational quickly — a SaaS tool can be configured in days, custom software takes months
- Your requirements are likely to change significantly in the next 12 months — building custom software for a moving target is expensive
- You do not have the technical leadership to oversee a software build and manage a development relationship
- Your current SaaS spend is under £1,000/month and growing slowly
When Custom Software Is Clearly the Right Choice
- Your combined SaaS spend exceeds £2,000/month and is growing 15%+ per year
- Your competitive advantage comes from operational processes that generic tools cannot model correctly
- You are losing significant staff time to manual workarounds between systems (more than 10 hours/week across the team)
- You have data security, compliance, or residency requirements that commercial SaaS platforms cannot meet
- You want to build proprietary IP — software you can eventually license, sell, or white-label
- You have 20+ staff relying on the system daily, making reliability and performance critical
The Build vs Buy Decision Framework (2026)
Use these five questions in order:
- Does a SaaS tool handle 80%+ of your requirements without significant workarounds? If yes, use it until your business grows out of it. If no, continue to question 2.
- Is your 5-year SaaS TCO greater than £100,000? If yes, a custom build almost certainly has positive ROI. If no, continue to question 3.
- Does your competitive advantage depend on proprietary processes that SaaS cannot model? If yes, custom software is strategically justified regardless of short-term cost. If no, continue to question 4.
- Do you have or can you access the technical leadership to oversee a build? If no, do not build custom software yet — find a trusted development partner first. If yes, continue.
- Can you commit to a 4–12 month build cycle and the ongoing maintenance responsibility? If yes, custom software is the right choice for your situation.
Frequently Asked Questions
Is custom software always more expensive than SaaS in year one?
Yes, almost always. A custom software project costs £30,000–£150,000+ upfront, while SaaS requires no upfront investment. The payback period is typically 2–4 years for businesses spending £1,500–£3,000/month on SaaS.
Can I start with SaaS and migrate to custom software later?
Yes, and this is often the right approach. Use SaaS to validate your processes and requirements, then build custom once you know exactly what you need and have the revenue to justify the investment. The migration adds cost but is manageable with proper planning.
What is "bespoke software" in the UK context?
In the UK, "bespoke software" and "custom software" are used interchangeably — both refer to software built specifically for your business rather than an off-the-shelf product. Bespoke is the more formal British English term; custom is more commonly used in US-influenced tech contexts.
How long does custom software last before needing a rebuild?
Well-built custom software with modern architecture typically has a useful life of 5–10 years before a significant rebuild is needed. With regular maintenance and incremental updates, some systems run productively for 15+ years. Poor architectural decisions or outdated technology stacks can force a rebuild in 3–4 years.
What is the ongoing cost of custom software after launch?
Budget 15–20% of the initial build cost per year for maintenance, hosting, security updates, and minor feature development. A £80,000 custom system costs approximately £12,000–£16,000/year to maintain — significantly less than the SaaS subscriptions it typically replaces.
If you are evaluating whether custom software makes sense for your business and want an honest assessment based on your actual numbers, talk to our team. We will walk through your current SaaS stack, calculate your real TCO, and give you a straightforward recommendation — including cases where we think you should stick with SaaS.