The ERP you installed ten or fifteen years ago solved the problems of that moment. But the company has grown, processes have become more complex, tax obligations — Verifactu, SII, B2B e-invoicing — require connectivity that legacy software does not have, and the original vendor no longer offers updates. At that point, maintaining the inherited system is not a neutral decision: every month of delay accumulates technical debt, compliance risk and hours of manual work that could be eliminated.
This article explains when an ERP migration is unavoidable, how to choose between the most common alternatives for Spanish SMEs — Sage 200, Odoo and Microsoft Dynamics 365 Business Central — and what phases a well-executed migration project involves.
Signs that your current ERP has reached its limit
Not every company needs to change systems at the same time. But there are symptoms that, when they appear together, indicate that migration is no longer optional:
- End of vendor support. Sage 50 Classic (the perpetual desktop version) has gone years without security updates in its older versions. Running unpatched software in an environment with access to customer and supplier data is a documented cybersecurity risk.
- Incompatibility with Verifactu and B2B e-invoicing. Royal Decree 1007/2023 (Verifactu Regulation), amended by RD 254/2025, and Royal Decree 238/2026 developing mandatory B2B e-invoicing (Ley Crea y Crece) require invoicing software to meet technical standards for traceability and interoperability that older ERPs cannot incorporate without a complete rewrite.
- Month-end closings that take days. If the monthly balance or bank reconciliation requires exporting data to Excel and cross-referencing it manually, the problem is not the team: it is that the software lacks sufficient integration.
- Inability to connect with e-commerce, CRM or logistics platforms. API integrations, standard in any modern ERP, are non-existent or extremely costly in legacy systems.
- Dependence on a single person. When only the most senior accountant knows how to use the system, the operational risk is enormous.
Sage 50 vs Sage 200 vs Odoo: a real comparison table
The decision of where to migrate depends on transaction volume, process complexity and available budget. The following table summarises the key factors for the three most common options among Spanish SMEs with 10 to 250 employees:
| Criterion | Sage 50 (legacy) | Sage 200 | Odoo 17 Community / Enterprise | Microsoft Dynamics 365 BC |
|---|---|---|---|---|
| Licence model | Perpetual (no recent updates) | Monthly subscription per user | Community: open source; Enterprise: subscription per user | Monthly subscription (Essential / Premium) |
| Deployment | Local Windows desktop only | On-premises or private cloud (SQL Server) | Cloud, on-premises or hybrid | SaaS Azure exclusively |
| Verifactu / SII | Not compatible in older versions | Compatible (update included) | Compatible via official module or partner | Compatible (Microsoft ISV marketplace) |
| API integrations | Very limited (CSV/ODBC export) | Partial REST API; Power Platform connector | Full JSON-RPC API; more than 16,000 modules | Native REST API; advanced Power Platform connector |
| Included modules | Accounting, invoicing, basic POS | Accounting, purchasing, sales, warehouse, production | Accounting, sales, purchasing, CRM, e-commerce, HR, manufacturing | Accounting, supply chain, sales, projects, service |
| Ideal company profile | Micro-enterprise with no planned growth | Industrial or distribution SME, 20-100 employees | SME with diverse processes or e-commerce, 10-250 employees | SME with Microsoft ecosystem (Office 365, Teams, Azure) |
| Implementation cost range | — | €15,000-60,000 depending on scope | €8,000-50,000 (Community) / €20,000-80,000 (Enterprise) | €25,000-100,000 |
Note: cost ranges are market guidelines and depend on the number of users, modules, data migrations and customisations. Request a detailed quote for your specific case.
When it makes sense to migrate to Sage 200
If your company already works with Sage 50 and the team is familiar with Sage's accounting logic, migrating to Sage 200 is the path of least friction. The vendor has designed the transition process with data converters that preserve the accounting history, customer and supplier master records, and the product catalogue.
Sage 200 is a particularly good fit for industrial, distribution or service companies with complex accounting needs (consolidated groups, multiple cost centres, project-based analytical accounting). Its native integration with Microsoft's Power Platform allows automation workflows to be built without custom development.
Sage 200's weakness compared to Odoo is modular rigidity: adding functionality outside the official catalogue requires vertical development by a partner, which raises costs and creates dependency. It also lacks a native e-commerce module, so if your online channel is significant you will need an external integration.
When it makes sense to migrate to Odoo
Odoo is the alternative that is growing fastest among Spanish SMEs with heterogeneous processes. Its strength is functional coverage in a single environment: the same system manages sales, CRM, warehouse, manufacturing, HR, e-commerce, accounting and projects, eliminating the need to maintain several disconnected applications.
The Community version (open source, no licence cost) is sufficient for many SMEs if the implementing partner covers Spanish localisations (VAT, SII, Verifactu, payroll). The Enterprise version adds official Odoo S.A. support, automatic updates and modules such as Studio (no-code customisation) and Sign (electronic signature).
Odoo makes sense when the company wants to replace several tools at once (ERP + CRM + online store + customer portal) and is willing to invest in a broader implementation project that, in return, eliminates duplicate licences and data silos.
If you want to know the technical difference between Odoo and the most common alternatives, our Odoo implementation for SMEs service page covers what each version includes and how we handle Spanish localisation.
The phases of an ERP migration project
An ERP migration is not simply installing new software. Data is the most critical asset and the riskiest part of the process. At Summum Sistemas we have been accompanying system-change projects at SMEs in Castilla y León and the Canary Islands since 2007, and the approach that works always follows the same phases:
Phase 1 — Diagnosis and process mapping
Before choosing a system, you need to understand what real processes the company has, what data exists in the current system (and what quality that data is in) and what integrations with third parties (bank, accounting firm, logistics operators, online store) must be maintained. This diagnosis takes between two and four weeks and includes interviews with key users from each area.
Phase 2 — Selection and configuration of the new system
With the process map defined, the test environment is configured. This is where modules are parameterised, approval workflows are designed, the chart of accounts is defined and document templates (invoices, delivery notes, quotes) are created. This is the time to make decisions about customisations: which are essential and which are work habits that are better adapted to the new system rather than replicated in code.
Phase 3 — Data migration
Data migration is the highest-risk phase. Data from the old system is rarely clean: there are duplicate customers, obsolete items, unreconciled account balances. Before migrating, active data cleansing is required. The technical process includes: extraction from the source system (CSV export, ODBC or API depending on the case), transformation to the target system's data model, loading into the test environment, and line-by-line validation of accounting balances and stock.
Phase 4 — Training and parallel operation
The most common mistake in migrations is skipping the parallel period. For two to four weeks (at least one full billing cycle), the company operates in both systems simultaneously. This allows discrepancies to be detected before they affect customers or the VAT return. Training is delivered by role: not all users need to know the same things about the new system.
Phase 5 — Cut-over and stabilisation
On the cut-over day (go-live), the old system is closed and the company operates exclusively on the new one. The first four weeks post-launch are critical: the partner must have high availability to resolve incidents in real time. After that period, the project enters normal evolutionary maintenance.
The three most costly mistakes in ERP migrations
After seeing migration projects of many different types, the failures with the greatest impact on cost and timeline are always the same:
- Underestimating the state of the data. Companies assume their database is clean because it has been in the system for years. The reality: duplicates, items with no real stock, unbalanced balances. A data audit before migration saves weeks of corrective work afterwards.
- Over-customising before knowing the system. The natural impulse is to replicate in the new system exactly what you had in the old one. The result: a system that is expensive to maintain and unable to take advantage of version improvements. It is better to adapt to the standard in the first implementation and only customise what is genuinely differentiating for the business.
- Not involving end users from the start. If the project is led only by IT or management, and the users who will use the system daily find out during the training week, change resistance and operational errors are guaranteed.
Verifactu and B2B e-invoicing: why they accelerate the decision
Royal Decree 1007/2023, which develops the technical Verifactu regulation, establishes that computerised invoicing systems must guarantee the integrity, conservation, accessibility, readability, traceability and immutability of invoicing records. The adaptation deadlines for companies not taxed under special IRNR arrangements are:
- Large companies (Corporate Income Tax contributors): mandatory adaptation before 1 January 2027 (deadline set by Royal Decree 254/2025 of 1 April 2025).
- Other companies and self-employed: before 1 July 2027.
An ERP that cannot be certified as a verified invoicing system (VERI*FACTU) forces the company to maintain two parallel systems or incur penalties. This requirement alone makes migration a legal obligation for many SMEs still using unupdated software.
If your company is also subject to SII (Immediate Supply of Information), the need for real-time integration with the AEAT is already a reality today. Modern ERPs include native or certified SII connectors; legacy systems require costly and unstable custom developments.
To explore this further, our ERP consultancy team at Summum Sistemas can assess whether your current system is or is not adaptable to Verifactu without changing platform.
Integration with automation and artificial intelligence
A modern ERP is not just a record-keeping system: it is the source of truth on which automated and intelligent workflows can be built. With an up-to-date system you can, for example, automate the bank reconciliation process, generate draft purchase orders based on minimum stock levels, or feed a real-time dashboard without exporting a single Excel file.
In this area, Odoo and Business Central have an advantage over Sage 200 thanks to their open APIs, which allow integrations with automation tools such as Power Automate or n8n. If process automation or the incorporation of artificial intelligence is part of your roadmap, also speak with our colleagues at Summum IA, who frequently work at the layer above these systems.
Frequently asked questions
How long does an ERP migration take in an SME?
It depends on data volume, process complexity and the number of integrations with third parties. As a general rule, a migration project from Sage 50 to Sage 200 or Odoo in a company of 20-50 employees takes between three and six months from the start of the diagnosis to a stable go-live. Projects with many customisations or complex data migrations may extend to nine months.
Can the accounting history be migrated to the new ERP?
Yes, though with caveats. The usual approach is to migrate the opening balances for the current financial year and the customer, supplier and item master records. The transaction history from previous years can be kept in the source system (in read-only mode) or migrated in a query format. Migrating full transactional detail for several years complicates the project and is usually unnecessary for day-to-day operations.
What happens to data if the migration goes wrong?
A well-executed project never decommissions the source system until the new one has been validated and is in stable production. During the parallel period, both systems coexist. The old system acts as a safety net. In addition, before any data migration, full and verified backups are taken. The risk of data loss in a professional migration is minimal; the real risk lies in improvised or self-executed migrations without a methodology.
Can I migrate from Sage 50 to Odoo directly, without going through Sage 200?
Yes. There is no obligation to migrate in steps. Many companies move directly from Sage 50 (or even from spreadsheets) to Odoo. The key is that the project includes the correct Spanish localisation — SII adapter, Verifactu module, PGCE chart of accounts — and that the data migration is carried out with a rigorous cleansing and validation process. The leap is greater in terms of habit change for users, but the functional benefits are also greater.