The verdict in three sentences
Inheriting 4 business applications built by a defunct agency is an immediate operational risk: with no documentation or updates, the first vulnerability or outage stops distribution. A fixed maintenance retainer costs, as a 2026 order of magnitude, EUR 1,500 to 6,000 per month per scope, versus EUR 550 to 700 per day on time and materials (in London, expect roughly 15 to 25% more, about GBP 550 to 750 per day), and the retainer wins once the need is recurring and predictable. The contract must impose a 4-hour SLA on blocking incidents, reversibility and quarterly dependency updates, for an annual budget of 15 to 25% of the build cost.
Retainer or time and materials: compare against your usage profile
Time and materials bills hours spent, a retainer bills a service commitment. The choice depends on how stable the need is and on your capacity to manage a vendor day to day.
| Criterion | Fixed retainer | Time and materials |
|---|---|---|
| 2026 price (Lyon benchmark) | EUR 1,500 to 6,000 per month | EUR 550 to 700 per day |
| Budget predictability | High, fixed amount | Low, depends on usage |
| Commitment | Contractual SLAs with penalties | Best-efforts obligation |
| Client-side management | Monthly steering | Weekly task tracking |
| Enhancements included | Day quota (2 to 6 per month) | All, billed by time |
| Best for | Stable production apps | Rebuilds, one-off projects |
| Main risk | Poorly defined initial scope | Drift in days consumed |
The most common setup among our clients combines both: a retainer for run and support, plus a quota of time-and-materials days for enhancements.
SLAs and clauses to require in the contract
A maintenance contract without measurable service levels protects nobody. These are market benchmarks for a distribution business app.
| Incident level | Example | Response | Resolution | Usual penalty |
|---|---|---|---|---|
| Blocking | Orders impossible, app down | 1 business hour | 4 business hours | 5% of monthly fee per 4 h block |
| Major | Key feature degraded, workaround exists | 4 business hours | 2 business days | 2% of monthly fee per day |
| Minor | Display glitch, slow export | 1 business day | Next release | None |
| Critical security (CVE) | Public flaw in a dependency | 4 h | 48 h | 5% of monthly fee |
| Dependency updates | Framework, libraries | Quarterly | Per schedule | Included |
Add three structural clauses: reversibility (code, access, documentation and 10 to 20 days of knowledge transfer at the end of the contract), ownership of code and hosting accounts in your name, and a penalty cap, usually 15 to 20% of the monthly fee.
Taking over orphaned apps: the audit phase
Before signing a retainer, any serious vendor runs a takeover audit: inventory of code and access, analysis of outdated dependencies, deployment tests, minimum documentation. Allow 5 to 10 days per app, or EUR 11,000 to 28,000 for four apps. That audit is what lets you set a fair retainer instead of a cautious, expensive estimate.
Mini case study
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Julien, CIO of a retail distribution group (figures from a Lyon case, transferable to London with a 15 to 25% uplift), takes over four apps (store orders, pricing, logistics, supplier portal) whose original build cost EUR 260,000. On time and materials, the previous year used 95 days at EUR 620, or EUR 58,900, with no response commitment. The takeover audit costs EUR 18,000. The retainer then negotiated is EUR 4,200 per month with 4 enhancement days included and a 4-hour SLA, EUR 50,400 a year, or 19% of build cost. The annual budget drops by EUR 8,500, the audit pays back in just over two years, and store orders now have guaranteed restoration within 4 hours.
FAQ
What annual budget should we plan for web app maintenance?
15 to 25% of the original build cost. For an EUR 80,000 app, that is EUR 12,000 to 20,000 per year.
What is a developer's day rate on time and materials?
EUR 550 to 700 per day in Lyon in 2026 for a senior profile at an agency, and roughly GBP 550 to 750 in London. An expert or architect costs EUR 750 to 950.
What does a reversibility clause cover?
Handover of source code, access, documentation and 10 to 20 days of knowledge transfer to the new vendor. It should be priced at signature.
Can we switch from time and materials to a retainer mid-year?
Yes, after a 5 to 10 day audit per app that sets the scope. The switch usually takes 4 to 6 weeks.
Are security updates included?
In a good contract, yes: quarterly dependency updates and critical fixes within 48 h, at no extra charge.
Let's scope your project. We audit your existing apps and propose a fixed or hybrid maintenance contract, with SLAs, reversibility and a costed annual budget. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
