TL;DR: custom software maintenance typically costs 15 to 25% of the initial development cost per year; for an SME business application, monthly packages on the French market run from €400 to €1,400 before tax in 2026, roughly €6,000 to €16,000 per year.
"And after delivery, who looks after it, and for how much?" is the most common objection from SME owners considering a tool built around their process. It is a fair one. Over a software product's lifetime, maintenance can account for up to 70 to 80% of the total investment, according to an analysis published by Swiss consultancy Edana on January 3, 2026. Comparing build quotes without asking what comes next means comparing half-prices.
Key takeaways
- The most cited budgeting rule puts annual software maintenance at 15 to 25% of the initial development cost (Edana, January 3, 2026).
- In France, a maintenance package for an SME web application runs from €400 to €1,400 per month before tax in 2026; hosting and monitoring, often billed separately, add €150 to €500 per month.
- According to a McKinsey survey of 50 CIOs, 10 to 20% of the technology budget earmarked for new products is diverted to resolving technical debt.
- Taking over an undocumented codebase after a vendor leaves costs €8,000 to €25,000: code ownership and documentation are negotiated in the development contract, not at divorce time.
How much does custom software maintenance cost in 2026?
For an SME business application, the maintenance budget most often lands between €6,000 and €16,000 per year before tax in 2026. The most widely used rule of thumb sets aside 15 to 25% of the initial development cost every year: a tool built for €30,000 therefore calls for €4,500 to €7,500 of annual maintenance, more if integrations are numerous or availability commitments are strict. The table below sums up the main cost lines observed on the French market.
| Cost line | 2026 range | Worth remembering |
|---|---|---|
| Monthly package (bug fixes + small changes) | €400 to €1,400 / month | About €6,000 to €16,000 per year for an SME web app |
| Rule as % of initial cost | 15 to 25% per year | A €30,000 tool calls for €4,500 to €7,500 per year |
| Time and materials | €500 to €750 / day | For changes outside the package |
| Hosting and monitoring | €150 to €500 / month | Often billed separately: check the contract |
| Taking over undocumented code | €8,000 to €25,000 | The real cost of a vendor who locks you in |
These ranges come from price grids published by French providers, including this 2026 comparison of application maintenance costs (source in French); treat them as benchmarks, not truth, and always get several quotes on an identical scope. Two options inflate the bill sharply: 24/7 on-call support, which adds 30 to 50% to the package and only makes sense for a genuinely critical application, and strict availability commitments, which absorb 10 to 15% of the maintenance budget according to Edana.
What does a maintenance budget actually cover?
The word "maintenance" covers three very different activities, and their split explains the price gaps. Corrective maintenance fixes bugs; it is the most visible share but usually the smallest. Adaptive maintenance keeps up with a moving environment: security updates, dependency upgrades, changes in third-party APIs (a payment provider, a messaging service); it weighs 20 to 30% of the annual budget according to Edana. Evolutionary maintenance, finally, adds features at the pace of real usage; it absorbs 40 to 60% of the maintenance budget of living software.
This breakdown leads to a counter-intuitive conclusion: "finished" software does not exist, because its environment never stops moving. Browsers, APIs and regulatory obligations change whether your code changes or not. The dial can be adjusted, though: a simple internal tool, with no web exposure and no external integration, can live with a minimal bug-fix baseline and a budget well below the ranges quoted. That is a case where the honest answer is not to sell a full package.
Why the bill blows up: technical debt
When a maintenance budget explodes, the cause is rarely the provider's daily rate; it is almost always accumulated technical debt. According to McKinsey's survey "Tech debt: Reclaiming tech equity", run with 50 CIOs, 10 to 20% of the technology budget meant for new products is actually diverted to resolving issues tied to that debt; a later McKinsey analysis estimates that it represents 20 to 40% of the value of surveyed companies' entire technology estate.
The case documented by Edana shows the mechanics: a Swiss industrial SME had budgeted 20% of its initial development cost for maintenance; undocumented technical debt and a component losing vendor support pushed that rate to 35% the very next year. Protection does not come from a better rate; it comes from the initial contract. Four clauses matter as much as the price: ownership of the code and access credentials (a Git repository in the client's name), handover documentation kept up to date, response times by severity level, and an exit cost written down in black and white. Without them, the French market prices the takeover of an undocumented codebase at €8,000 to €25,000.
Is an off-the-shelf SaaS cheaper than maintained custom software?
Often, yes. A SaaS subscription is pooled maintenance: the vendor spreads the cost of fixes, security updates and new features across thousands of customers. If a market tool covers your need for a reasonable subscription, keeping it is the right call, and no maintenance math will change that conclusion.
Maintained custom software becomes rational in three situations: when the subscription stack grows past the cost of a single tool (six SaaS products at €300 per month is €21,600 per year, every year, forever); when the process is too specific to fit a generic tool; and when owning the data and the code matters, for compliance or strategic-dependency reasons. The fair comparison is never "quote versus subscription": it is total cost against total cost over 3 to 5 years, counting price hikes and extra seats on one side, the initial build plus 15 to 25% per year on the other.
How I scope maintenance with my clients
In my practice as a freelance consultant and developer, maintenance is scoped before the first line of code, not after delivery. The code belongs to the client from day one: a Git repository in their name, admin access, handover documentation delivered at go-live. Concretely, that means the exit cost is close to zero; any developer can take the project over, and that freedom is precisely what keeps the relationship healthy. Changes then run through a monthly retainer at the pace of real usage, and a well-scoped fix fits in a sprint from €400 before tax; the rest is quoted per project.
A good share of upkeep also automates very well: monitoring, backups and alerts are set up at go-live, often with n8n automation building blocks. The automated press-monitoring system built for Fromagerie Ermitage runs on that principle: a workflow that runs on its own, watched by alerts, with human upkeep kept to a minimum. That is where the craft is heading: fewer billed hours spent repairing, more systems that flag their own drift.
Custom software is not a purchase; it is an asset you keep in working order, like a vehicle or premises. The question to ask any provider before signing is therefore not just "how much is the build?" but "what happens the year after, and what belongs to me if we part ways?".
You can run the exercise right now on your current tool: who owns the code, where is the documentation, and what would switching providers cost? If any of those answers is fuzzy, a 30-minute call is usually enough to clear it up: book a slot. The full framework (code delivered to the client, retainer, handover) is detailed on the custom web app page.
Frequently asked questions
What annual budget should you plan for custom software maintenance?
The most widely used rule sets aside 15 to 25% of the initial development cost every year. For an SME business application, monthly maintenance packages on the French market run from €400 to €1,400 before tax in 2026, roughly €6,000 to €16,000 per year, with hosting often billed separately.
Is maintenance mandatory for custom software?
Nothing makes it contractually mandatory, but unmaintained software degrades: dependencies age, security flaws go unpatched, third-party APIs change. A simple internal tool can live with a minimal bug-fix baseline; for an application exposed on the web or connected to external services, skipping maintenance eventually costs more than paying for it.
What should a maintenance contract contain?
Four clauses matter as much as the price: ownership of the code and access credentials (a Git repository in the client's name), up-to-date handover documentation, response times by severity level, and an exit cost written into the contract. Taking over an undocumented codebase after a vendor leaves costs €8,000 to €25,000 according to French market benchmarks.
Is an off-the-shelf SaaS cheaper than maintained custom software?
Often, yes: a SaaS subscription is maintenance pooled across thousands of customers. If a market tool covers the need for a reasonable subscription, keeping it is the right call. Custom software becomes rational when the subscription stack grows too large, the process is too specific, or owning the data matters; the fair comparison is total cost of ownership over 3 to 5 years.