Custom ERP or Spreadsheet? How to Know It's Time to Switch

Spreadsheets don't stop working overnight. They start costing you in ways that don't show up in any cell: hours spent reconciling, errors nobody catches until month-end, and one person without whom nothing closes. Before you buy an ERP or commission one, it pays to pin down what exactly is failing, because sometimes the answer is a better spreadsheet.

Signs your spreadsheet has hit its limit

• There are several versions of the same file, and nobody's sure which one is the source of truth.
• Only one person understands the formulas. When they're on vacation, the close stops.
• Money is calculated by hand or with formulas copied row by row: interest, commissions, late fees. A row still carrying last year's formula doesn't warn anyone.
• You can't tell who changed what, or when, and sometimes that matters a lot.
• Several people enter data at once, or from a phone in the field.
• Customers, partners or suppliers need to see their part, and today you email it to them.
• The file takes forever to open. An Excel sheet tops out at 1,048,576 rows by 16,384 columns, but the problems above show up long before that.

If one or two of these sound familiar, tidying up may be enough. If it's four or more, you're already paying for a system; you're just paying in staff hours.

Three paths

A better spreadsheet

The most underrated option. One master file in the cloud with version history; data entry kept apart from calculations; dropdowns instead of free text; protected sheets and a named owner. It's cheap and it buys time. It's enough when few people use it, the calculations aren't sensitive and the process rarely changes.

Off-the-shelf ERP

Odoo, NetSuite, SAP Business One, Microsoft Dynamics 365 Business Central and many more. You get proven modules, updates and support. Some have open versions: Odoo, for instance, offers an open-source Community edition and a licensed Enterprise edition. The trade-off is that you adapt to the way the software works, and every customization has to be looked after through every upgrade. It fits when your process is standard: purchasing, inventory, accounting, payroll.

Custom ERP

Built around your process, including the part that makes you different, and the code is yours. The trade-off: you pay to build it and to maintain it, and you need documentation and tests so it doesn't depend on a single person. It fits when what you do doesn't fit a standard module, especially when money is calculated with rules of your own.

An example from our portfolio: the ERP Axen Energy uses internally to run its solar financing and lease contracts. It handles collections with late fees calculated daily, produces PDF account statements and runs a 12-stage sales pipeline with a portal for installers. None of those rules came in a standard module.

There's also a middle path: an off-the-shelf ERP for accounting and invoicing, plus a custom module for what's unique to your business, connected to each other.

What drives the cost of running each one

Prices depend on the case, so we won't throw numbers around, but these are the factors that weigh most:

• Licenses. For off-the-shelf systems, usually per user and per module, every year.
• Implementation and data migration. For all of them. Cleaning up years of historical data is usually the biggest surprise.
• Change. Your process will change. With off-the-shelf software, customizations can complicate upgrades; with custom software, every change is development work.
• Integrations. With your accounting software, your bank, your online store or WhatsApp. If you operate in Mexico, add the provider that stamps your CFDI invoices.
• Hosting, backups and security. Someone has to own them.
• Training. A system nobody knows how to use is back in a spreadsheet before long.
• Continuity. Who maintains it if the developer leaves? Code in a repository under your company's name and up-to-date documentation are what protect you.

Why tests matter when money is involved

In a spreadsheet, a broken formula fails silently. In a well-built system, each business rule has automated tests that run before every change: if the late fee on a sample contract should come to a certain amount and now comes out different, the change doesn't reach production until someone understands why.

That's why, when there are financial calculations, tests aren't a luxury. Axen Energy's ERP carries more than 2,200 automated tests. The number on its own proves nothing; what matters is that it lets you change a rule without fear of breaking what already worked.

Ask whoever proposes a system which tests run before each change, and ask them to show you.

How to migrate without stopping the business

Often the hard part isn't the software but the migration. What works best:

• Live data first. Open customers, contracts or orders. History can come later, or stay available as read-only in the old spreadsheet.
• One period in parallel. Run the new system alongside the spreadsheet for a full cycle and compare the results. Every difference gets explained before the file is retired.
• A cutover date. From that day on, data goes only into the system; the spreadsheet becomes read-only.
• Role-based training. Using each person's real cases, not a generic manual.

How to decide

Four questions help more than any feature comparison:

1. Is your process standard, or is it exactly what sets you apart?
2. How many people use it, and from where: the office, the field, your customers?
3. What happens if a calculation is wrong for a whole month?
4. Who will maintain it three years from now?

If the process is standard, start with off-the-shelf. If it's yours and it moves money, consider custom or a hybrid. If it's small and stable, clean up the spreadsheet and check again in a few months. And if part of the problem is plain repetitive data entry, maybe what you need first is to automate that step.

If you'd like another opinion

We're happy to look at your file with you and tell you which of the three paths we'd take, no strings attached. See how we build systems on Web & App Development, or reach us through contact. And if you don't have an in-house tech team, you may want to read about forward-deployed engineering.