The verdict in three sentences
For a business application delivered for USD 75,000 to 190,000 (GBP 60,000 to 150,000), budget annual maintenance at 15 to 20% of the build cost, which means a retainer of USD 900 to 3,500 or GBP 700 to 2,600 per month. An SLA-backed retainer (blocking incidents picked up within 4 business hours) protects a mid-market company better than pure time and materials, which stays useful for one-off enhancements. Demand a reversibility clause and up-to-date documentation at signature, or you will pay twice the day you switch vendors.
Retainer, time and materials or SLA contract: what you are really buying
Application maintenance covers three kinds of work: corrective (fixing defects), preventive (security patches, framework and dependency upgrades) and evolutive (small functional changes). The billing model decides who carries the risk.
| Model | Indicative 2026 price (UK / US) | Who carries the risk | Best for |
|---|---|---|---|
| Time and materials | GBP 500 to 750 / USD 700 to 1,100 per day | Client | Ad hoc changes, variable budget |
| Simple monthly retainer | GBP 700 to 1,300 / USD 900 to 1,800 per month | Shared | Stable app, under 50 users |
| SLA-backed retainer | GBP 1,300 to 2,600 / USD 1,800 to 3,500 per month | Vendor | Critical app, multi-site company |
| Prepaid day bank | 10 to 20 days/year, 5 to 10% discount | Client | Planned enhancements |
| Per-ticket contract | GBP 80 to 150 / USD 100 to 200 per ticket | Shared | Low incident volume |
| Managed hosting + maintenance | + GBP 250 to 1,000 / USD 350 to 1,400 per month | Vendor | Hosting and on-call included |
The low end of the day rate usually means a mid-level developer outside London or a nearshore team; the high end means a senior engineer or a London or New York agency. Time and materials looks cheap until something breaks: a blocking incident on a Friday evening with no contractual on-call can freeze your operations all weekend.
The service levels to write down in black and white
A retainer without an SLA is a verbal promise. The contract must define severity, response time and resolution time, with service credits.
| Severity | Example | Response | Target resolution | Typical service credit |
|---|---|---|---|---|
| Blocking | App down, invoicing stopped | 4 business hours | 1 business day | 5% of monthly fee per day late |
| Major | Module unavailable, workaround exists | 8 business hours | 3 business days | 2% per day |
| Minor | Display glitch, slow export | 2 business days | Next release | None |
| Critical security | CVE in a dependency | 24 h | 72 h | 5% per day |
| Enhancement | New field, new report | Quote within 5 days | Per roadmap | None |
Cap service credits at around 15 to 20% of the monthly fee: beyond that, serious vendors decline or inflate their price. Add a monthly report (open tickets, SLA compliance, updates applied): it is your only way to check the retainer is being spent usefully.
Reversibility and documentation: the most valuable clause
Reversibility organises the exit: handover of source code in your Git repository, hosting access, deployment scripts and current technical documentation. Plan a 5 to 10 day transition billed at the contract day rate, plus an obligation to assist the incoming vendor for 1 to 3 months. Check intellectual property too: custom code must be assigned to you, only the vendor's generic components stay under licence.
What to require: a Git repository owned by your company from day one, architecture documentation of at least 15 to 30 pages, automated test coverage targeting at least 60% of business code, and a dependency inventory with versions.
Mini case study
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Sarah, CIO of a 420-employee distribution company in Manchester, has just received a route planning application built for GBP 75,000. The vendor offers time and materials at GBP 600 per day. On a comparable application last year, the team consumed 26 days: 26 × 600 = GBP 15,600, with no response commitment. The SLA-backed alternative costs GBP 1,180 per month, GBP 14,160 per year (18.9% of build cost), with 22 days included, 4-hour response on blocking incidents and a defined exit plan. Sarah saves GBP 1,440 and shifts on-call risk to the vendor. The 4-day gap is covered by a prepaid day bank at GBP 560.
FAQ
What percentage of build cost should I budget for maintenance?
The 2026 order of magnitude is 15 to 20% per year. A USD 125,000 application therefore needs USD 19,000 to 25,000 of annual maintenance, hosting excluded.
Can a different vendor maintain the app than the one who built it?
Yes, provided you hold the code, documentation and access. Expect a 5 to 15 day takeover phase, roughly USD 3,500 to 16,000 depending on codebase size.
What happens to unused retainer days?
It depends on the contract: some roll over up to 20% of days to the next quarter, others forfeit them. Negotiate a limited rollover rather than a straight loss.
Are security updates included in a retainer?
They should be, as preventive maintenance. A major framework upgrade (often 3 to 8 days of work) is frequently excluded and quoted separately.
What commitment length should I accept?
12 months renewable with 3 months' notice is standard. Avoid 36-month commitments with no exit clause tied to SLA breaches.
Let's scope your project. Send us your application's scope, incident volume and response requirements, and we will price retainer, time and materials and SLA options side by side. 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.
