Excel, ERP or custom app: which one for what?
Spreadsheets, ERPs and custom apps answer different needs. Which for what, and why most companies need two of the three.
By Jérôme Knops
Published September 15, 2026 · Updated September 20, 2026 · 6 min read
The question is almost never “which one?” It's “which one for what?” A spreadsheet, an ERP, and a custom app don't replace each other. Each one does one thing very well and everything else poorly. The trouble starts when you ask one of them to do another's job.
Excel: perfect for thinking things through, fragile for teamwork
The spreadsheet is unbeatable at one thing: laying out a problem, running a calculation, testing an assumption. It's already on every computer, everyone knows how to use it, and it costs nothing extra.
It falls short as soon as several people work on the same data:
Versions multiply
“Quote_tracking_v3_final (2)” gets passed around by email, and nobody knows which one is the real one.
The same data gets retyped several times
The client in the quote, in the schedule, on the invoice.
Nothing warns you
A spreadsheet doesn't follow up on a quote or flag a project that's stuck.
Keep it for one-off calculations, simulations, and analysis. Don't rely on it for tracking that several people update every day.
The ERP: the backbone, not the field tool
The ERP holds what has to be accurate: accounting, inventory, invoicing, purchasing. It's the system of record, and it should stay that way.
It falls short where the work actually happens:
Entering data is cumbersome
For anyone on a job site, in a warehouse, or on the road.
- Documents arrive by email and get retyped by hand, field by field.
Every change goes through the integrator
It goes through them, with a wait and a quote each time.
Keep it for business management and accounting. Don't ask it to be the everyday tool for people who aren't in the office.
The custom app: the missing layer between the two
A custom app doesn't replace the spreadsheet or the ERP. It does what neither of them does: it follows the way you work, with your own steps and your own terms, and it moves information between the people who produce it and the people who need it.
- Data entered once, reused everywhere.
- Simple data entry on the phones of the people on site.
- Automations: follow-ups, alerts, documents that are read and then sent into the ERP.
It makes sense when the time lost retyping, searching, and following up costs more than the app does. It doesn't make sense if your business fits into off-the-shelf software, or if your team is under five people.
The three side by side
Read the table row by row, not column by column: none of the three wins everywhere, and that is exactly the point.
| Spreadsheet | ERP | Custom app | |
|---|---|---|---|
| What it holds best | a calculation, a simulation | the system of record: inventory, purchasing, accounts | daily work and how it moves |
| Who handles it | one person at a time | the back office | the field, from a phone |
| Time to change something | instant | an integrator's quote | a few days |
| What it costs | nothing extra | a license per user, every month | a setup fee, then a subscription |
| Where it breaks | with the second person | as soon as you leave the office | if an off-the-shelf tool would have done the job |
The most common case: all three at once
Most of the companies we meet already run all three, and that is not a failure. The ERP keeps the accounts, a spreadsheet prepares the decisions, and some in-house app — sometimes just a form — fills the gap between them.
What costs money is not owning three tools. It is entering the same data three times. A packing slip retyped by hand is a few minutes per document, multiplied by a year's volume — and it is the line item you see least, because it is spread across everyone.
So the right move is not to drop a tool. It is to find where information gets retyped, and remove the retyping.
What each one costs, in orders of magnitude
The three are not measured on the same scale, and that is what most often distorts the decision.
- The spreadsheet is already paid for. Its cost is invisible: it shows up as hours of retyping and errors found too late, never on an invoice.
- The ERP is paid per user, per month, indefinitely. Every field worker you would like to connect adds a license — which is usually why they never get connected.
- The custom app is paid once to build, then maintained. With us, between €2,500 and €9,000 excl. VAT to go live, then €290 to €690 excl. VAT per month, with no per-user cost on top.
That last line is what changes the math once you have twenty people in the field: a per-head subscription eventually overtakes a one-off build, and the crossover arrives sooner than people expect.
How to tell what you're missing
Three questions are usually enough.
| If you answer yes to… | You're probably missing… |
|---|---|
| “We never know which version is the right one” | a shared tool, not another spreadsheet |
| “What comes in by email gets retyped into the ERP” | a layer that reads the documents and sends them there |
| “Nobody knows where a project stands without calling” | an app built for the field |
If off-the-shelf software does the job, go with it. We'll tell you so, and it does happen.
How we step in, in practice
We replace neither your spreadsheet nor your ERP. We build the third layer, the one that lives next to the field: simple entry from a phone, data entered once and reused everywhere, and access that depends on each person's role.
In practice, your ERP keeps the accounts and receives what the app sends it. Your spreadsheets keep serving to think with. What disappears is the copying between the two. See how we build that layer, and what we decline to do.
Excel, ERP or custom app: key takeaways
The spreadsheet is for thinking things through, the ERP is for keeping the books, and the custom app is for keeping the work moving. Most of the companies we meet keep their ERP and their spreadsheet, and add the layer they're missing between the two.
Before you choose, put a number on what your current way of working costs you. That number, not the feature list, tells you whether one more tool is worth it.
Frequently asked questions
When should you move away from Excel?
When several people update the same tracker every day. The spreadsheet remains unbeatable for framing a problem, running a calculation, testing an assumption. It breaks down as soon as versions multiply, the same data is re-typed several times, and nothing warns you when a file is stuck.
What is the difference between an ERP and a custom application?
The ERP is the backbone: it holds inventory, purchasing, accounting, and it imposes its rules — that is its strength. The custom application lives at the point of contact with the field and the daily decision, where an ERP is weak by nature. They do not replace each other: the right answer often includes both.
Can you have all three at once?
That is the most common case, and it is not a failure. Excel for simulations, the ERP as system of record, a custom application for what neither can do. What costs money is not having three tools: it is re-keying the same data into all three.
How do you know which one you are missing?
Look at where the information you need to decide actually lives. If it is in an inbox or in somebody's head, a tool is missing. If it is in the ERP but unreadable or a day old, a layer above is missing. If it is in a spreadsheet three people edit, an application is missing.
Founder and CTO of Edenio
Jérôme Knops is the founder of Edenio, where he designs and builds custom business applications for construction, supply chain and distribution companies. He runs the scoping meetings, writes the code, and stays the person you talk to once the tool is in production.
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