The short answer: less often than you are told. A full custom ERP is justified in a handful of cases, and almost none of them involve a business under 50 people.
The reason is not the upfront cost. It is that an ERP never finishes — legislation, tax rules, banking, new requirements. With an off-the-shelf system the vendor pays for those; with custom, you do.
Want an assessment before you decide?
Tell us what systems you run today and we will tell you whether the problem can be solved without a new ERP.
When it is justified and when it is not
| Situation | Decision |
|---|---|
| Standard trading or production operation | Off-the-shelf ERP |
| A distinctive process in one or two places | Off-the-shelf + custom modules |
| The process is the competitive advantage | Custom is worth examining |
| A sector with no suitable product on the market | Custom is worth examining |
| “We do not like the interface” | Not custom |
| “It will work out cheaper” | Almost never true |
The third row is the real criterion. If the way you price, route or produce is what sets you apart, forcing it into a packaged product can cost you the advantage.
In every other case the question is not “custom or off-the-shelf” but “which off-the-shelf, and how much configuration” — the wider framing of that decision is in custom software versus off-the-shelf tools.
Which modules you actually need
Most proposals include twice what will be used.
| Module | Needed from |
|---|---|
| Finance and invoicing | Day one |
| Stock and warehouse | If you hold physical products |
| Purchasing and suppliers | 20+ suppliers |
| Production | If you manufacture |
| Customers and sales | Often covered by a CRM |
| HR | 30+ people |
| Management reporting | Always, but after the rest |
Start with two modules, not seven. An implementation covering everything from day one is the commonest cause of failure — the team cannot keep up with the learning and reverts to the old way.
If your problem is only stock, you may not need an ERP at all: see inventory management.
What it costs, realistically
| Approach | Upfront | Annual | Time |
|---|---|---|---|
| Off-the-shelf ERP, standard install | €5,000–20,000 | Subscriptions | 2–4 months |
| Off-the-shelf with substantial configuration | €20,000–60,000 | Subscriptions + support | 4–8 months |
| Custom ERP | €60,000+ | 15%–20% of the build | 9–18 months |
These ranges are indicative of the market and shift — confirm with quotes.
The “annual” column is what decides it. An €80,000 custom ERP typically costs €12,000–16,000 a year in maintenance and adjustments — and that continues for as long as the system runs.
Add to it: data migration, training, and the first two months of reduced productivity that nobody puts in the quote.
Have a quote in front of you?
Send us the proposal and we will tell you what is missing from the calculation.
The middle options people overlook
Between “off-the-shelf as it comes” and “everything from scratch” there are three routes:
- Off-the-shelf ERP with custom modules at the one or two points where you differ. The commonest correct answer.
- Good systems, connected. Accounting, warehouse and CRM talking to each other cover many mid-sized businesses.
- Phased replacement. One subsystem at a time, with the old one running alongside.
The third reduces risk more than any other decision. Replacing every system simultaneously on one date is the scenario with the most failures.
What to check before signing
- Ownership of code and data. In writing, with no ambiguity.
- The ability to export all your data in an open format.
- What happens if the vendor disappears. Documentation, access, handover.
- Compliance with tax obligations and e-invoicing.
- The cost of changes after delivery, with an hourly rate in writing.
The third is the most dangerous point in a custom project. A system only one company understands ties you to that company for as long as it runs.
How to scope and commission the work: outsourcing software development, and what the specification should say: technical requirements.
Frequently asked questions
How long does an implementation take?
Off-the-shelf: 2–4 months. Custom: 9–18 months to full operation.
Can we start with a few modules?
Yes, and it is the recommended approach. Two modules in live use are worth more than seven in testing.
What happens to our existing data?
It gets migrated, but how clean it is determines the time. Budget separately for that.
Do we need an internal owner?
Yes, without question. Without somebody with time and decision-making authority, the implementation slips.
Is e-invoicing integration mandatory?
Transmission obligations apply and continue to evolve. Confirm with your accountant what applies to your business before choosing a system.
The first step
Write down the three processes costing you the most time today, and next to each: is it done in a standard way, or in your own way?
If all three are standard, you do not need a custom ERP — you need the right choice and a competent implementation, and that costs a fraction.
Next step
Book a free 30-minute call with the team at The Dev Alley. We will look at your processes and tell you which route your business can carry.