Custom SaaS vs off-the-shelf subscription for an SME in London: the 2026 math

The verdict in three sentences

An off-the-shelf SaaS is unbeatable at launch and becomes expensive at scale because you rent forever and own nothing. Custom software costs more in year one but pays back around 2.5 years as soon as your user count grows or your need drifts from the standard. The real question is not price, it is the specificity of your process and the ownership of your data.

The raw math over 36 months

Take a London SME with 30 users. A mainstream business SaaS commonly bills 25 EUR net per user per month in 2026. Custom software is an upfront investment followed by maintenance.

Over 3 years off-the-shelf stays cheaper. But two variables change everything: user growth (every extra seat costs forever) and the paid modules the vendor keeps adding. At 60 users, the subscription doubles to 1,500 EUR/month while custom barely moves.

What the price does not tell you

The headline cost hides structural gaps. These criteria weigh as much as the euro per month.

A standard SaaS imposes its data model: if your business has a quirk (an atypical approval workflow, an in-house commission calculation, a proprietary ERP integration), you pay for manual workarounds every week. Custom absorbs that quirk once.

Mini case study

Thomas runs a 42-person B2B services SME in London. He uses a market CRM at 29 EUR per user per month for 40 seats, i.e. 13,920 EUR/yr. His team spends about 6 h/week re-keying data between that CRM and their invoicing tool for lack of native integration: at a loaded cost of 35 EUR/h, that is 10,920 EUR/yr of wasted time. A custom CRM integrated with invoicing is quoted at 48,000 EUR + 6,000 EUR annual maintenance. From year 1 he saves the subscription and the re-keying, i.e. 24,840 EUR/yr. The custom build pays back in ~2.2 years, after which he saves over 24,000 EUR every year while owning his tool.

FAQ

From how many users does custom become worthwhile? As a rule beyond 25-30 active users, or sooner if the subscription exceeds 20 EUR per seat per month. Below 15 users, off-the-shelf almost always wins.

Is the 2.5-year break-even universal? No, it is a 2026 order of magnitude for a 45,000 EUR build against a 750 EUR/month subscription. It drops to 18 months if headcount grows fast, and rises to 4 years for a small, stable need.

Can I start off-the-shelf then migrate? Yes, and it is often wisest: validate the need on a rented tool for 12-18 months, then internalise with custom once the process is stable. Check export reversibility before signing.

Who owns my data in each case? With an off-the-shelf SaaS your data lives with the vendor under their terms; with custom, the database and code are yours, which is decisive for compliance and any resale.

Is custom riskier? The risk is not the technology but the vendor: demand source code, documentation and a reversibility clause. A well-scoped project cuts risk far more than a subscription does.

Let's scope your project. Tell us your user count, your current subscription and your process quirks: we compute your exact break-even and a fitted custom scope. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.