The verdict in three sentences
A maintenance retainer is not a side budget line: it is the guarantee that your B2B website stays available, secure and up to date after launch. In London in 2026, expect 100 to 950 EUR/month depending on service level, with a price gap that mostly reflects the SLA and included evolution hours. Sign on the written scope, not the verbal promise: the devil is in the on-call clause.
The three maintenance retainer tiers in 2026
Maintenance covers three distinct blocks: corrective (bugs, security), preventive (updates, backups, monitoring) and evolutive (small improvements). Here are the ranges observed in the London market for a brochure site or a light business application.
| Tier | Price/month | Included scope | Evolution hours | SLA |
|---|---|---|---|---|
| Basic | 100 - 180 EUR | CMS updates, weekly backups, security patches | 0 h | Best effort, 48 working hours |
| Standard | 180 - 400 EUR | + 24/7 monitoring, daily backups, priority support | 1 - 2 h | 99.9% uptime, 8 h restore |
| Premium | 400 - 950 EUR | + On-call, recovery plan, quarterly audit | 3 - 5 h | 99.95% uptime, 4 h restore |
| Ad hoc | 100 - 160 EUR/h | One-off intervention on request | — | No commitment |
A classic trap: a basic tier with no evolution hours turns every small request (page add, form tweak) into ad-hoc billing. Over twelve months, an active site easily consumes 10 to 20 hours of small changes.
The scope and service levels to negotiate
A serious SLA quantifies three measurable commitments. Without these figures, the clause is worthless in a dispute.
| Metric | Definition | 2026 standard level | Typical penalty |
|---|---|---|---|
| Uptime | Monthly availability rate | 99.9% (max 43 min downtime/month) | Credit 5% of fee per 0.1% missed |
| Restore time | Guaranteed time to recovery | 4 h (critical), 8 h (major) | Credit 10% per breached tranche |
| Response time | Guaranteed acknowledgement | 1 h in working hours | Automatic escalation |
| Backups | Frequency + retention | Daily, 30 days | Quarterly tested restore |
| Reporting | Activity report | Monthly (incidents, time spent) | — |
Require that penalties be capped but real (invoice credit, not just an apology), and that reversibility is planned: at contract end you recover code, access and backups within 15 days.
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Mini case study
James, IT director of a 90-person industrial SME in London, hesitates between the basic tier (150 EUR/month) and the standard (330 EUR/month) for his new B2B catalogue site. In year one on basic, he pays 1,800 EUR in retainer, but 14 hours of evolutions and two out-of-hours incidents cost him 2,100 EUR extra ad hoc, totalling 3,900 EUR. The standard tier would have cost 3,960 EUR all-in, with monitoring and 8 h restore. Real gap: 60 EUR over the year for far superior service. James switches to standard.
FAQ
What is the difference between maintenance and hosting? Hosting (15 to 120 EUR/month) covers the server; maintenance covers code, updates and support. Some premium tiers include managed hosting, others bill it separately.
Is a maintenance retainer mandatory? No, but an unmaintained B2B site accumulates security holes and technical debt. A CMS left un-updated for 18 months often costs 2,000 to 5,000 EUR to bring back up to standard.
Can I cancel easily? Negotiate a 1 to 2 month notice period and a reversibility clause. Avoid 36-month commitments with no exit.
Are unused evolution hours carried over? Often yes over 1 to 3 months. Get it in writing: without a clause, hours are lost each month-end.
How do I actually measure uptime? Require a third-party monitoring tool (UptimeRobot, Pingdom) with read access, not just the vendor's word.
Let's scope your project. Describe your site (CMS, traffic, criticality) and target service level: we scope the right retainer, from 150 to 700 EUR/month. 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.
