SAP ECC to Dynamics 365 migration: timeline and cost

A migration from SAP ECC to Dynamics 365 Finance and Supply Chain Management typically takes 9 to 18 months for a single company and 18 months or more for a group rolling out in waves, so a business that wants to be live before SAP's standard maintenance ends on 31 December 2027 should already have chosen its direction, and a company deciding in late 2026 will most likely need SAP's paid extended maintenance to cover part of the journey. The cost is driven less by licences than by three items every ECC exit shares, whatever the target: rebuilding years of ABAP custom code, mapping the SAP data model to a new one, and running both systems side by side while the switch happens. That last point is what most boards miss.

Moving to S/4HANA is not an upgrade that avoids these costs. It is a reimplementation of comparable scale, which means the honest comparison is not "migrate or stay" but which platform the company wants to run on for the next ten years. This article sets out where the months go in a SAP ECC to Dynamics 365 migration, how the cost structure differs from S/4HANA and from staying on ECC, when a staged two tier approach makes sense, and when S/4HANA remains the better answer. It is written for CFOs, CIOs and finance transformation leads who need a defensible position before the 2027 deadline narrows their options.

Key facts at a glance:

• Deadline. SAP mainstream maintenance for ECC ends on 31 December 2027; extended maintenance to the end of 2030 costs two percentage points more per year.
• Market position. Gartner estimated that only 39 percent of about 35,000 ECC customers had moved to S/4HANA by the end of 2024.
• Timeline. 9 to 18 months for a single company, 18 months or more for a group migrating in waves.
• Effort. Both S/4HANA and Dynamics 365 are reimplementations: custom code is rebuilt and data is remapped either way.
• Cost model. SAP perpetual licences carry about 22 percent annual maintenance; Dynamics 365 is a per user subscription with updates included.
• Staged path. A two tier model keeps headquarters on SAP while subsidiaries move to Dynamics 365 first.

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How long does a SAP ECC to Dynamics 365 migration take?

For a midsize company running SAP ECC in one or two legal entities, a migration to Dynamics 365 Finance and Supply Chain Management usually takes 9 to 18 months from the first assessment to a stable go live. The lower end applies to organisations with a contained footprint: finance, controlling, purchasing and sales, a manageable volume of custom code and a limited number of interfaces. The upper end applies when production planning, warehouse management and industry specific extensions are in scope, or when years of ABAP modifications have to be unpicked before anyone can say what the business actually needs. Groups with many company codes rarely move in one step and plan in waves, which puts the full programme at 18 months or more.

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What surprises most leadership teams is that the configuration of Dynamics 365 is rarely on the critical path. The schedule is set by three pieces of work that have nothing to do with the target system: understanding what the current ECC landscape actually does, translating its data into a different model, and keeping the business running while two systems overlap. The table below shows how a typical programme divides its time, and why the first two rows deserve more attention than they usually get.

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Why is 2027 a decision point rather than a cliff?

SAP's standard maintenance for ECC and the wider Business Suite 7 ends on 31 December 2027. Customers can buy extended maintenance until the end of 2030 at a premium of two percentage points on top of their existing maintenance fee, which UpperEdge calculates as a relative uplift of about 9 percent on a 22 percent Enterprise Support rate. That option is designed for companies already in conversion to S/4HANA, and it covers core applications only. For large and complex landscapes moving to RISE with SAP, Forrester reports a further transition option running to 2033, but SAP has made clear it is not a blanket offer.

The deadline therefore does not switch ECC off. What it does is change the economics of waiting. Every year on ECC after 2027 costs more, buys less, and leaves legal and regulatory updates increasingly to the customer. At the same time the market for migration capacity is tightening: Gartner, quoted by CIO, estimated that around 17,000 ECC customers could still be on the old platform in 2027, all competing for the same consultants. Companies that decide in 2026 negotiate from strength, choose their partner and their window, and keep the option to move in stages. Companies that decide in late 2027 take whatever capacity and terms are left.

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Is S/4HANA an upgrade or a reimplementation?

The most persistent misunderstanding in ECC planning is that S/4HANA is the low effort path because it carries the SAP name. In practice a move to S/4HANA is a reimplementation: a new data model built around the Universal Journal, a new database, a redesigned user experience and, in most cases, a new commercial model under RISE with SAP. Even a technical conversion, the so called brownfield route, forces companies to remediate custom code that no longer fits the simplified data structures, and many organisations that start brownfield end up redesigning core processes anyway because the old ones no longer make sense on the new platform.

Once both options are understood as reimplementations, the decision changes character. The question stops being how to protect the investment in SAP and becomes which platform deserves the next decade of the company's processes, data and skills. That framing favours a fact based comparison over loyalty. ABAP modifications built over fifteen years cannot be carried into either target unchanged, so the cost of cleaning them up is incurred regardless of direction. What differs is what the company gets afterwards: the licensing model, the update cycle, the extension approach, the ecosystem of tools the workforce already uses, and the availability and price of the specialists needed to run it. Those are the criteria a board should be weighing.

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Where does the time go in a SAP to Dynamics 365 migration?

The first block of time goes into the custom code inventory. A mature ECC system often holds thousands of custom objects, from reports and user exits to entire bespoke transactions, and a large share of them is no longer used or is already covered by standard functionality in Dynamics 365. Sorting them into retire, replace with standard, and rebuild as an extension is detailed work, but it is also the single biggest lever on cost: every object retired here is an object nobody has to design, build, test and maintain. Programmes that skip this step tend to rebuild the past, line by line, on a platform that did not need it.

The second block is the data model. SAP and Dynamics 365 describe the same business differently: company codes become legal entities, cost centres and profit centres become financial dimensions, the material master is split into products and released products, and pricing conditions map to trade agreements. Each of these translations needs decisions from finance and operations, not just technical mapping. The third block is reconciliation: several full migration rehearsals, each checked against the ECC trial balance and open items down to the last cent, before anyone signs off a cutover. The fourth is coexistence, because few companies can switch every entity and interface on one weekend, so integrations have to support both systems for a while.

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How does the cost of Dynamics 365 compare with S/4HANA and staying on ECC?

The three options carry very different cost profiles, and comparing headline licence prices hides most of the difference. Staying on ECC looks cheap in the short term but carries rising maintenance charges, shrinking support scope and the growing cost of keeping old infrastructure and scarce ABAP skills. S/4HANA under RISE with SAP bundles software, database and hosting into one subscription, which simplifies the bill but does not include the implementation, and Gartner puts S/4HANA migration costs anywhere from about 2 million dollars to as much as 1 billion dollars for the most complex enterprises, according to the same CIO report.

Dynamics 365 Finance and Supply Chain Management is billed per user per month, with cheaper licences for occasional roles and no separate database or server licences, and with Microsoft's regular updates included rather than sold as future upgrade projects. The implementation effort is broadly comparable to S/4HANA because the same custom code and data work has to be done. The decisive difference shows up in years two to ten, long after the implementation invoice has been paid: the cost of updates, of extensions built outside the core, of reporting and analytics, and of hiring people who can run the platform. The table summarises how each cost element behaves.

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Can we migrate in stages instead of all at once?

Yes, and for international groups a staged path is often the most sensible way to manage risk. In a two tier model the headquarters stays on SAP for now, while subsidiaries, newly acquired companies or new markets go live on Dynamics 365 one by one, with integrations feeding results and master data back to the centre for consolidation. Each wave has its own scope, testing and go live criteria, so a problem in one country does not halt the group, and by the time the decision about the headquarters is due, the organisation already knows the new platform and its partner already knows the organisation. The same logic works by process: finance first, operations second.

A staged approach is not always the right one, and Dynamics 365 is not always the right destination. Being clear about this is part of a credible business case, and it protects the board from a decision that has to be reversed later, at far greater cost than the original analysis. A partner that only ever recommends its own platform is giving the board a sales pitch, not advice, and the comparison should be run on the company's own landscape rather than on vendor brochures. S/4HANA usually remains the stronger choice in the following situations:

• Deep industry solutions. Core processes depend on SAP industry modules with no close equivalent elsewhere.
• Very large single instance. One global system serves many thousands of users with tightly coupled processes.
• Recent RISE commitments. Contractual obligations already signed make a platform change uneconomic.
• SAP centred ecosystem. Key partners, customers or regulators exchange data through SAP specific processes.

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How does ANEGIS approach SAP ECC migrations?

ANEGIS starts every SAP ECC engagement with a free comparative analysis, before any licence is purchased: an inventory of modules, ABAP customisations, integrations and data, followed by a fit gap review of Dynamics 365, S/4HANA and staying on ECC on the same facts. If the data points away from Dynamics 365, the recommendation says so. Once a direction is chosen, the migration runs on a methodology based on Microsoft Success by Design, with decision gates and architecture reviews at each stage, phased go lives starting with finance or with individual subsidiaries, and several full data migration rehearsals reconciled to the balance before cutover.

Two details matter to finance leaders in particular. Historical ECC data is moved to a Microsoft Fabric analytical layer, so it stays available for reporting and audit without keeping a decommissioned SAP system alive. And compliance for Polish entities is covered by ANEGIS's own KSeF, JPK and Polish Localisation Pack solutions, maintained in house. ANEGIS has worked on the Microsoft Dynamics platform for more than 13 years, and 90 percent of its clients stay with it after go live. Its reimplementation experience includes enterprise scale programmes such as TERG, where Dynamics 365 Finance and Operations became the central financial platform for 14 group companies and about 400 stores, with more than 40 integration interfaces. More detail is on the SAP ECC to Dynamics 365 migration page.

Plan your move from SAP ECC

If you need a defensible recommendation before the 2027 deadline, Contact ANEGIS to book a free comparative analysis of your ECC landscape.

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