Short answer: the 4 phases of 90 days
You can split a move from Excel to an ERP into four phases over 13 weeks: discovery (weeks 1-2), setup and data migration (3-6), testing and training (7-10) and go-live and support (11-13). This plan is a general framework we prepared for a small manufacturer going live with a first module; it is not the timeline of a real customer project, and it does not mean "you will go live in 90 days".
To keep expectations realistic, one limit: according to Panorama Consulting's 2025 ERP Report (172 respondents, January 2024 to January 2025) the median project timeline was 9 months; more than half of the respondents were multinational organizations, so that number does not map one-to-one onto a small manufacturer. Time grows with scope (number of modules, customization, number of sites). 90 days makes sense as a target for a first slice, not for the whole ERP.
| Week | Phase | Key output |
|---|---|---|
| 1-2 | Discovery | Process and data inventory, scope, project owner |
| 3-4 | Setup | Configuration, code and chart-of-accounts standard |
| 5-6 | Data migration | First trial migration, cleanup list |
| 7-8 | Testing | Second trial migration, end-to-end workflow test |
| 9-10 | Training | User training, acceptance test |
| 11 | Cutover preparation | Final migration plan, transaction freeze date |
| 12 | Go-live | Final migration, reconciliation, day-one support |
| 13 | Support | Intensive support, first fixes |
Be clear from the start about why you are leaving Excel. In audits compiled by Raymond Panko (the "Core 5" study, 55 spreadsheets), 91% of the spreadsheets contained serious errors; the sample is small and the work is old, so that figure does not mean every Excel file is wrong, but it shows the risk of leaving critical business data in hand-maintained formulas.
Weeks 1-2: process and data discovery
What will we move to the ERP, and what will we leave?
The job of the first two weeks is not to write code or install software but to map the current situation: which Excel files exist, which process does each serve, and which formulas and macros carry business rules? In manufacturers, the bill of materials (BOM), routings, stock codes, work orders, lot or serial tracking and cost calculations typically live in separate files. You do not have to bring all of it into the first slice: look at which process causes the most trouble and choose the first module accordingly.
Who owns the Excel files?
Name one owner for each dataset: write down who verifies the stock cards, the bill of materials, the customer list. A record without an owner is a record nobody answers for when migration goes wrong. Bring your accountant into the process at this stage too: clarify early how your e-Invoice, e-Archive and e-Ledger obligations affect the ERP choice (which modules, which integrator); for current thresholds, check the announcements of the Turkish Revenue Administration (GİB) and your accountant. This article is not financial or legal advice.
Weeks 3-6: setup and data migration
How do we clean the data?
This is the riskiest part of the plan. In Panorama's 2025 report, the most common reason for projects running over schedule was data issues: data integrity, consistency and accuracy. In the previous year's report the most common reason was resource constraints, so the ranking does not stay the same every year, but it shows that data preparation has never been unimportant. Our recommendation: remove duplicate records, bring stock and customer codes to one standard, decide where opening balances come from and track the cleanup list weekly.
Why run more than one trial migration?
The first trial migration almost always finds errors, and it should. We recommend two trial migrations: one in weeks 5-6 and one in weeks 7-8; in the second, verify that the errors found in the first round are gone. Compare record counts and balance totals with the Excel source (reconciliation) as you go.
How are open items loaded?
Open work orders, receivables and payables and pending orders are loaded separately on cutover day. Decide in advance which jobs will be finished in the old system and which will continue in the new one; without that decision, lost work orders appear in the first week.
Weeks 7-10: testing and training
How do we test?
Do not look at screens one by one; run an end-to-end workflow: a real scenario with real data in which an order turns into stock movement, a work order, shipment and an invoice. The test should be done not only by the person who set up the system but by the people who will use it every day. Prepare an acceptance list: which scenarios must pass before you go live?
Who gets trained, and when?
In a post based on its 2025 research, Prosci writes that organizations put 92% of their ERP budget into technology, while human factors were found to matter 6x more than technical factors in improving ERP benefits. Prosci sells change management consulting and "6x" is a count of recommendations; still, it is a reminder that the training plan deserves as much attention as the technical setup. Do not squeeze training into the days just before go-live: deliver role-based training in weeks 9-10 and have department leads trained first.
Do we need to run in parallel?
According to a Panorama Consulting article dated 26 December 2024, a "big bang" approach generally works best for organizations with one or two functional areas and can be faster and cheaper for a small organization if the risk is acceptable; with multiple locations or units, a phased go-live is usually more practical. Running the old and new systems side by side can increase operating cost (system maintenance, extra training, temporary integration tools). With a narrow scope, switching in one go makes sense; still, verify critical reports against the old source in the first weeks.
Weeks 11-13: go-live and support
How do we plan cutover day?
Cutover day should not be a day of surprises: write down in advance the transaction freeze date (the moment no new records are opened in the old system), the final migration time, the reconciliation steps and the rollback condition. Choose a weekend or a low-load period; avoid seasonal peaks.
What happens in the first weeks after go-live?
The first weeks are when questions and fixes peak. So ask for the support period and response times in writing in the contract; plan week 13 not as "the project is over" but as an "intensive support week". The plan for the second module starts after this.
Common mistakes
- Leaving data preparation to the end. In Panorama 2025 the most common reason for delay was data issues; start cleanup in week 3.
- Underestimating training. The project does not end when the technical setup ends; if users do not adopt the system, the benefit does not come.
- Growing the scope. In Panorama's 4 March 2026 study, additional technology needs were named as the main cause of budget overruns; keep the first slice narrow and leave additions to a second phase.
- Talking to the accountant late. e-invoicing compliance affects the ERP choice; bring the accountant in from the first week.
- Treating 90 days as a guarantee. This plan is a framework; data quality, scope and team capacity determine the time.
Frequently asked questions
How many months does it take to move from Excel to an ERP?
In Panorama Consulting's 2025 ERP Report the median project timeline is 9 months; more than half of the respondents were multinational organizations, so it does not map one-to-one onto a small firm. Time depends on the number of modules, customization and data quality. The 90-day plan above is a framework aimed at taking the first module live, not the whole ERP.
What causes the most problems in data migration?
According to Panorama 2025 the most common reason for projects running over schedule was data issues: integrity, consistency and accuracy. In practice, duplicate records, inconsistent stock and customer codes and Excel files without an owner are where that problem comes from.
Do we need to run in parallel?
It is not mandatory, but it has a cost. According to Panorama, running the old and new systems together can raise operating cost; for small organizations with one or two functional areas a one-time switch can be faster and cheaper. Comparing critical reports against the old source in the first weeks is a reasonable middle path.
What if employees resist?
According to Prosci's research, human factors are decisive for ERP benefits, and resistance often comes from lack of information. Bring department leads in early, deliver training by role and before go-live, and name one person they can ask in the first weeks.
To discuss a migration plan that fits your process, get in touch. If you are wondering what to ask an ERP vendor, see our 12 questions to ask when choosing an ERP vendor in Izmir.
Sources: The 2025 ERP Report (Panorama Consulting Group), Big Bang ERP Implementation (Panorama Consulting, 26 December 2024), Panorama Consulting 2026 ERP implementation outcomes press release (4 March 2026), Audits of Operational Spreadsheets (Raymond Panko), ERP project management and implementation success (Prosci)
Cover photo: EqualStock / Unsplash