In this guide 6 sections
Move in phases when your sheets feed each other and staff cannot stop work for a weekend. Choose a single cutover when the data is small, self-contained and one team owns it. Phasing costs more sync effort. A single cutover leaves a thinner rollback. Pick by what you can afford to lose.
What each approach actually means
A phased move shifts one area at a time. Customers go first, then stock, then billing. Each area leaves its workbook only when the new system holds it reliably.
A single cutover freezes every sheet on a chosen evening, loads the lot, and starts the next morning on the new system. Nothing is half-moved. That is its appeal and its danger.
Neither is better in general. The choice depends on how tangled your files are. A quick look at the VLOOKUP formulas between tabs tells you a great deal.
- Phased: one module live at a time, old and new run side by side
- Single cutover: one freeze date, one load, one go-live
- Hybrid: a pilot branch first, then everyone else together
Where sync risk bites
Phasing means two sources of truth for weeks. A customer’s credit limit lives in the new screen while the invoice register still sits in Invoices_2026.xlsx. Someone edits the wrong one and the totals drift.
Control this with a rule for each field: one owner, one place. Mark the retired sheet read-only the day its area goes live. Rename it with a suffix such as _FROZEN so nobody opens it by habit.
Cutover has almost no sync risk, because the old files stop on day one. Its risk moves elsewhere: a bad mapping is discovered after everyone has started typing.
Staff load and rollback
Phasing spreads training over months. The stores clerk learns the stock screens while accounts carries on in Excel. Nobody is overwhelmed. The team does live with two ways of working for longer than they would like.
The cutover is one hard week. Everyone trains together, and the first Monday is noisy. The upside is a clean finish and no lingering double entry.
Rollback differs sharply. In a phased move you can pause after any step and still have a working business. After a single cutover, going back means re-keying every transaction entered since the freeze.
- Keep a dated backup copy of every sheet before its freeze
- Write down the rollback trigger before go-live, not during it
- Name one person who may call a rollback
- Log every entry made after the freeze so it can be replayed
Which sheets can stay as spreadsheets
Not every workbook deserves migration. A one-off quotation calculator, a personal pivot table or a quarterly board summary can stay in Excel. They read from the system rather than feed it.
Move anything that several people edit, anything that others look up by customer code or part number, and anything an auditor asks for. Shared and referenced files cause the real damage.
Leave the rest alone, and say so in writing. A short list of retained sheets, with an owner for each, stops the migration from swelling.
- Move: shared registers, price lists, stock ledgers, receivables
- Keep: personal analyses, one-off calculators, archived years
- Review later: anything fed only by an export from the new system
A simple way to decide
Count the links. If three or more sheets look up the same master list, phase it, starting with that list. If the data lives in one file with one owner, a single cutover is usually enough.
Then test your appetite for rollback. Ask what happens if invoicing stops for two days. If the answer is a serious problem, phase.
Finish by writing a one-page plan: order of areas, freeze dates, rollback trigger and the sheets that stay. Circulate it to the team leads this week and ask each to mark what is missing.
Migration approach decision sheet
This sheet fits on one page and has four blocks. The first lists every workbook with its owner, editors and the sheets that look it up. The second scores sync risk, staff load and rollback need from one to five. The third records the chosen approach and freeze dates. The fourth lists sheets that stay as spreadsheets, with a reason.
Open a blank worksheet to printQuestions owners ask
Is a phased migration always safer than a single cutover?
No. Phasing keeps rollback easy but doubles the entry points for weeks. If the data is small and one team owns it, a single cutover avoids that drift and finishes sooner.
How long should old and new run together?
Long enough to close one full cycle, such as a month-end, with matching totals. Stop earlier and you have not tested the reports. Stop much later and staff drift back to the sheets.
What do we do with the old spreadsheets afterwards?
Mark them read-only, rename them with a frozen suffix and store them with the backup. Keep them for the period your records policy or auditor requires, then archive them.
Can we start with just customers?
Yes, and it is a common first step. Customer codes are looked up by almost every other sheet, so a clean master list pays back quickly even before stock or billing move.