Software maintenance and support: what you pay for

What keeps changing under a finished system, where maintenance money goes, and eight things a support agreement should say.

Updated 4 October 2026 · 8 min read

The short answer

Software maintenance is the work that keeps a finished system safe and useful: security updates, fixing faults, keeping up with the systems around it and changing it as the business changes. UK firms usually buy it as a monthly retainer, and the market benchmark is 15 to 25 per cent of the build cost a year.

Most of that money goes on improvements, not repairs. In the best-known study of maintenance work, 60 per cent of the effort went on changes users asked for and 17 per cent on fixing faults.

Most owners with a Windows 10 computer heard about 14 October 2025, the day Microsoft stopped sending it security fixes. A bespoke system is built from dozens of parts like Windows, each with its own end date, and nobody writes to tell you when one passes.

What changes under a system nobody touches

The parts it is built on. Every system is written in a programming language and assembled from ready-made parts, and each version of those has an end date, like Windows 10. Version 8.1 of PHP, the language behind a large share of business websites, stopped getting security fixes on 31 December 2025, and version 8.2 follows on 31 December 2026. A system on an expired version keeps working. It just stops being protected against newly found holes.
The certificate behind the padlock. The certificate that tells a browser your web address is genuine used to last up to 398 days. Since 15 March 2026 the limit is 200 days, from March 2027 it is 100, and from March 2029 it is 47. Renewing it by hand once a year no longer works, so renewal has to be automatic, and somebody has to notice when it fails.
The systems it connects to. Xero, Shopify, Sage and the rest change the way outside systems connect to them on their own timetable, not yours.
Phones and browsers. Both update every year, and app stores set deadlines of their own, which the app cost guide lists.
The business. Prices, products, rules and staff change, and the system has to follow them.

None of these is a fault. They are why a system finished in 2024 needs work in 2026 when nobody has reported a problem.

Where maintenance money goes

Kind of work	What it looks like	Share of effort
Improvements users ask for	A new report, an extra field, a slow screen made quicker	60%
Keeping up with what changes around it	New versions of the parts it is built on, a connected system changing	18%
Fixing faults	Something that worked has stopped, or never worked properly	17%
Everything else	Work that fits none of the above	4%

From a 1978 survey of application software managers by Lientz, Swanson and Tompkins, still the most quoted split. A 2003 study of three individual systems found at least twice as much time going on faults, so treat it as a guide.

When you buy support, remember that a retainer covering only faults buys the smallest slice of the work. Robert Glass, summing up decades of studies, put maintenance at 40 to 80 per cent of what software costs, 60 on average, and most of it is the business asking for something new.

Eight things a support agreement should say

How quickly they respond and how quickly they fix, for each level of priority. A reply within the hour that says "looking into it" meets a response time and fixes nothing.
What counts as a fault and what counts as a change. Without that line, every disagreement turns into an argument about which one it was.
How fast security updates are applied. Ask for a number, such as "high-risk fixes within 14 days". "As needed" commits them to nothing.
How the system is backed up, and when a restore was last tested. A backup that has never been restored may not restore.
Who is told when the system stops working, and how quickly. You should not be the person who notices.
Whose name each account is in: hosting, domain, certificates, app stores. It should be yours.
How and when the price changes.
How you leave: the notice period, and a handover of the system, everything needed to run it and the documentation. Software project rescue shows what happens without one.

What it costs

The market benchmark is 15 to 25 per cent of the build cost a year, and UK studios that publish their prices quote figures inside that range. On a £40,000 system that is £6,000 to £10,000 a year, or roughly £500 to £830 a month. The cost guide puts it next to the other running costs.

Systems connected to many others sit at the top of the range, because each connected system changes on its own timetable. Self-contained ones sit at the bottom. Every build we take on includes the first thirty days of fixes after launch, and the retainer starts after that if you want one.

When you do not need a retainer

The system is small, self-contained, used by a handful of people and holds nothing sensitive. Pay the original builder by the hour when something comes up, and ask them to check the updates once a quarter.
You employ a technical person who can apply updates and knows the system.
The system is due to be replaced within a year. Keep it safe, spend nothing on improving it, and put the money into the replacement.

Common questions

What is software maintenance?

The work that keeps a system safe and useful after it goes live: applying security updates, fixing faults, keeping up with changes in the systems and devices around it, and changing it as the business changes. Most of the effort usually goes on the last of those.

What is the difference between support and maintenance?

Support usually means answering questions and fixing things that go wrong. Maintenance means keeping the system current and changing it over time. Most retainers sell both, so read what is actually included rather than the name on it.

How much does software maintenance cost in the UK?

The common benchmark is 15 to 25 per cent of the original build cost a year, so £6,000 to £10,000 a year for a £40,000 system. Systems that connect to many others cost more to maintain than self-contained ones. Our own retainers are £750 and £2,200 a month.

What happens if we stop paying for maintenance?

Usually nothing, at first. The system keeps working while the parts it is built on stop receiving security fixes and the systems around it move on. The cost arrives later and all at once, when something breaks or a fix is needed urgently and several years of updates have to be caught up first.

Can a different company support software someone else built?

Yes, if you can give them a copy of the system and access to where it runs, and if you own it or have the right to have it changed. A careful company will spend a few days reading it before agreeing a price.

Is maintenance included in the price of a build?

Usually only for a short period after launch, to fix faults in what was delivered. Ours includes thirty days. After that it is a separate agreement, and it should be optional.