The verdict in three sentences
In 2026, budgeting maintenance for a custom app at 15 to 20 % of the build cost per year is the reference rule. The run covers fixes, enhancements, security updates, hosting and monitoring, not just bug repair. Ignoring the run means letting an app decay until a rewrite that costs 50 to 100 % of the original build.
Run components and annual budget
The table uses an app built for EUR 100,000 as reference. The amounts are 2026 orders of magnitude.
| Component | Share of run | Annual cost (EUR) |
|---|---|---|
| Corrective (bugs, incidents) | 25 % | 4,000-5,000 |
| Enhancements (small features) | 40 % | 6,500-8,000 |
| Security & dependency updates | 15 % | 2,500-3,000 |
| Hosting & infra | 10 % | 1,800-4,000 |
| Monitoring & alerting | 5 % | 900-1,500 |
| Management & reporting | 5 % | 900-1,500 |
| Total maintenance (15-20 %) | 15,000-20,000 |
For a EUR 100,000 build, expect EUR 15,000 to 20,000/year. A critical app with a strong SLA can reach 25 %.
SLA levels and price impact
The commitment on availability and recovery time drives the run price.
| SLA level | Availability | Critical recovery time | Uplift vs base |
|---|---|---|---|
| Best effort | not guaranteed | business day | baseline |
| Standard | 99.5 % | 8 business hours | +10-15 % |
| Business | 99.9 % | 4 business hours | +25-35 % |
| Critical | 99.95 % | 2 h 24/7 | +50-80 % |
A critical 24/7 SLA mobilises on-call staff: it's only justified if one hour of downtime costs more than the annual uplift.
Mini case study
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Claire, CFO of an industrial SME in Lyon, must budget the run of a management app built for EUR 120,000. She hesitates on the SLA level.
- Base maintenance at 17 %: 120,000 x 0.17 = EUR 20,400/year.
- Business SLA (+30 %): 20,400 x 1.30 = EUR 26,520/year, i.e. +EUR 6,120.
The app drives logistics: a half-day outage costs around EUR 9,000 in delays. The Business uplift (EUR 6,120/year) is recouped on the first outage avoided. Claire chooses the Business SLA.
FAQ
How much does custom app maintenance cost? Count on 15 to 20 % of the build cost per year. For a EUR 100,000 project, that's EUR 15,000 to 20,000/year.
Is maintenance just about bugs? No. Corrective work is only 25 % of the run. Enhancements, security, hosting and monitoring make up the rest and prevent obsolescence.
What happens without security maintenance? Dependencies age and vulnerabilities pile up. A deferred major update can then cost several weeks of dev instead of a few spread-out days.
Is a strong SLA always worth it? No. A critical 24/7 SLA (+50-80 %) is only justified if one hour of downtime costs more than the uplift. Otherwise, a Standard 99.5 % SLA is enough.
Can I smooth the run budget? Yes, via a monthly maintenance retainer. For a EUR 100,000 build, that's about EUR 1,250 to 1,700/month, predictable and controllable.
Let's scope your project. Send us the build cost, the app's criticality and the SLA level you want: we'll quote a clear maintenance retainer, component by component. 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.
