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Release date: 17 September 2025
A core banking system (CBS) is at the heart of every bank: it integrates essential banking processes such as account management, payment processing, lending and risk management, while securely and reliably administrating key components of the bank’s legal data.
Banks change their CBS in the course of mergers and acquisitions or when the existing system is outdated, no longer meets regulatory requirements, doesn’t support new business models or products, lacks in performance or engenders excessive maintenance costs. Changing the core system of a bank is highly complex: peripheral systems, processes, organization and infrastructure need to be adapted to the new system. This is exactly where zeb’s experienced team comes in: with more than 50 successfully completed core banking system migrations under their belts, our experts have the necessary expertise to smoothly transition your bank, its data and processes to a new CBS. Lukas and Theresa know what needs to be considered during a CBS migration. The two of them give you an exclusive insight into the main event in any CBS migration: the cut-over weekend.
Lukas has already supported several CBS migrations and is currently in charge of a software development project that is preparing a bank’s online banking system for instant payments.
Theresa has been a consultant at zeb since 2021 and advises clients on a wide range of IT topics – from bank start-ups and post-merger integrations to the implementation of new software solutions.
The process of a CBS migration typically follows these phases, some of which may overlap or run in parallel:
strategic considerations regarding the positioning of the bank and its particular features, e.g. weighing custom developments against standardization, analysis of the current system and collection of the requirements for the new system as well as selection criteria.
selection of the new core banking system based on the criteria defined in step 1 and negotiation of the contracts with the provider of the respective CBS.
detailing of the defined requirements in order to create a clear basis for the overall project plan.
adaptation of the new system to the specific needs of the bank, or adjustment of the bank’s processes, data, organization and infrastructure to the new system or state-of-the-art standards.
training the employees in using the new system.
extensive testing of the new system to ensure that all features work correctly.
transfer of data from the old system to the new one, including data cleansing and validation and go-live of the new system.
assistance with all downstream tasks as well as troubleshooting.
Our zeb teams support the client from the start of the project to its completion or in specific stages, depending on requirements. Experienced experts are on hand for each phase and specialist department to provide targeted assistance. Since the CBS is the central nervous system of a bank, which maps all processes and contains all data and transactions, we as consultants come into contact with all banking-related topics during a CBS migration. Such migration projects are therefore often referred to as the ideal “training project”, as they offer junior consultants both comprehensive, broad training and the opportunity to develop into specialist experts from an early stage. The accompanying overarching functions such as PMO, quality assurance and testing are also set up across the entire project and therefore the entire bank. This provides us with broad methodological knowledge that we can apply again and again in a wide variety of roles and projects!
Over the entire migration period, the bank’s and zeb’s teams are working towards one defined point in time: the cut-over. This involves the final changeover from the old to the new core banking system – including the final data migration and go-live. The cut-over usually takes place at the weekend to minimize disruption to bank operations. Everyone involved will be there on that weekend: the bank’s project management and team members, the CBS provider’s team, zeb consultants and often also the bank’s board members. The cut-over weekend is meticulously prepared well in advance to ensure that everything runs smoothly.
Weeks and months in advance, the cut-over team compiles all the necessary steps and processes to create a detailed migration plan that covers both the time frames of each activity and the persons responsible. A dress rehearsal simulates the weekend in order to test and adjust the plan. Contingency plans are developed so that everyone knows how to react in the event of problems. Communication and coordination are crucial – contact lists, reporting chains and on-call services are organized and communicated.
The zeb team often stays in the same hotel for the weekend and agrees who will be where and when. We make sure that all tasks are clear, set up a “cut-over chat” for live updates if required (and lift the mood with a tailor-made playlist. In Theresa and Lukas’s project, for example, it was classics like “Wo war ich in der Nacht von Freitag auf Montag? War ich drei Tage wach oder einfach beim CO?” – Where was I on the night from Friday to Monday? Was I awake for three days or simply at the CO?).
The control center plays a key role during the cut-over weekend: it stays on top of everything, coordinates all activities and responds immediately in the event of problems. The team consists of members of the cut-over team, project management, technical experts and quality assurance. They usually work together on premises to act quickly and efficiently.
A shift system with on-call duty guarantees that qualified staff are available at all times. The atmosphere is marked by a strong sense of community – everyone is working toward a common goal: a successful transition. Colleagues whose tasks have been completed often support other teams proactively or provide refreshments. Lukas and Theresa particularly remember the delicious “Quarkbällchen” (little doughnut balls).
Immediately after the cut-over, it’s all joy and pride: the team has been working towards this moment for months, and now it’s all done. As a rule, the zeb team goes straight into follow-up mode while the bank can start to develop routines with the new system.
As soon as everything has settled down, it is time for a joint meal or event to celebrate the zeb team – that way, we get a chance to look back on the time we spent together on the project, and when you say goodbye to the team, you fully realize what you have achieved together ...
The cut-over weekend is the highlight of every CBS migration. It showcases how close the team has become and how it has mastered challenges and celebrated successes. It can be hard to say goodbye to a project team, but thanks to recurring zeb events such as zeb.Uni, PG meetings or the Christmas party, keeping in touch is easy.
Would you like to experience the special atmosphere of a cut-over weekend in person? Then apply as a Consultant in Digital Transformation and IT Strategy. We look forward to getting to know you and working on innovative projects together!
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