Today is exactly six months before Microsoft ends extended security updates for Windows 10. If your organization still has legacy Office files — .xls, .xlsm, .mdb, .mde — this is the planning window that matters.
Six months is enough time to do this properly. It is not enough time to ignore it and then panic in September. This guide gives IT teams a month-by-month roadmap to get from "we probably have some old files somewhere" to "we're fully migrated and ready for Windows 11."
The most common misconception: "My .xls files will still open after EOL." They probably will — for a while. The risk is more subtle than a hard break.
Here's what actually happens as you move machines to Windows 11 after EOL:
.xls file from email becomes a real security exposure.None of this is hypothetical. These are the exact issues LegacyLeaps was built to solve — and the organizations that hit them hardest are the ones that waited until after the deadline to start planning.
This plan assumes you're starting today. Each month builds on the last. If you're reading this later in the year, compress the early months and skip to wherever you are.
You cannot migrate what you haven't found. Run a full file system audit across every shared drive, file server, SharePoint library, and sampled set of local machines. Search for: *.xls, *.xlsm, *.xlsb, *.mdb, *.mde, *.accde. Log every hit with path, size, last-modified date, and owner.
Sort your inventory into three tiers. Tier 1: files actively used in business workflows (daily or weekly). Tier 2: files used occasionally (monthly or quarterly). Tier 3: files that haven't been opened in 2+ years. Tier 1 and Tier 2 are your migration targets. Tier 3 candidates for archival. Flag any file with macros, ActiveX, or Jet SQL queries as "complex" — they need more time.
Take your top 10–20 Tier 1 files and run them through conversion in a test environment. LegacyLeaps's free scan shows you exactly what's in each file — formulas, named ranges, VBA modules, ActiveX controls — before you touch anything. Run conversions, hand the output to the business owners who use those files daily, and get sign-off that the converted versions work. Resolve edge cases now, not in September.
With your pilot process validated, scale to all critical files. For large organizations, consider LegacyLeaps's bulk token packages (10, 25, and 50-file packs) — significantly cheaper than per-file pricing. IT Teams bundles are available for department-scale migrations. For complex Access databases with custom business logic, LegacyLeaps's done-for-you service handles conversion and validation end-to-end.
Complete Tier 3 decisions: convert, archive, or delete. Train staff on any workflow changes introduced by the migration. Update any automation scripts, scheduled tasks, or IT documentation that reference legacy file paths or formats. Document the few files you chose to archive instead of convert, and ensure a compatible viewer is available for them.
Re-run the file system audit to confirm no active-use legacy files remain. Archive originals (keep them, just not in active workflows). Complete your Windows 11 migration rollout for any remaining Windows 10 machines. On October 14, you're done — not scrambling.
LegacyLeaps scans your files and shows exactly what's inside — formulas, VBA modules, ActiveX controls, Jet SQL queries — before you commit to migration. Free, no account required.
Try the Free ScanNot all legacy files are equal. These are the ones that cause the most trouble during Windows migrations:
| File Type | Common Issue | Migration Complexity |
|---|---|---|
.xls with VBA |
Macros calling deprecated Windows APIs | Medium — LegacyLeaps preserves and audits macros |
.xls with ActiveX |
Controls lose registration on Windows 11 | Medium-High — requires re-registration or replacement |
.mdb with Jet SQL |
32-bit ODBC driver issues on Windows 11 | High — Jet SQL must be validated against ACE engine |
.mdb with forms/reports |
UI may require manual re-verification | Medium — form logic preserved, visual testing required |
.xls formulas only |
Row/column limits, named range handling | Low — straightforward conversion |
The most dangerous files are the ones you don't know exist. The accounting department's FY2008-reconcile-FINAL-v3.xls that runs the monthly close process — it's probably not on anyone's migration list because no one told IT it existed. Thorough discovery is non-negotiable.
A file can appear to open successfully in Excel while silently failing in ways that matter. Macros that previously called Windows API functions may not throw errors until a specific workflow is triggered. Validate functionality, not just open-ability.
Access migrations tend to get paralyzed by the question "should we modernize to a web app?" That's a valid long-term goal, but it doesn't have to block the immediate EOL migration. Convert .mdb to .accdb now to get off the legacy format. Consider modernization separately, on your own timeline.
Opening each file, saving as a new format, and hoping for the best is how you miss the hidden VBA module that breaks payroll calculations. Use a tool that reads the file structure and explicitly inventories what it contains — not just the file extension.
Some files genuinely can't be converted without losing functionality — typically Access databases with deeply customized VBA automation or complex multi-table Jet SQL that has no clean equivalent in .accdb format.
For these, you have three options:
If you're managing legacy file migrations for multiple clients, the next six months will test your capacity. A few things that help:
The files themselves don't break immediately at EOL. But as you migrate machines to Windows 11, compatibility layers for legacy Office formats get thinner. Some .mdb databases require the 32-bit Access Runtime, which has known issues on Windows 11. VBA macros may hit API deprecation warnings. The risk grows with every Windows update after EOL.
No — but you should inventory them all. Files actively used in business workflows should be migrated. Archived files can often stay in .xls format as long as you retain a compatible viewer. The priority is identifying which files your team depends on and ensuring those work in a Windows 11 environment.
Simple files with formulas and data: seconds. Files with VBA macros, ActiveX controls, or complex named ranges: minutes to an hour for validation. LegacyLeaps's free scan tells you exactly what's in each file before you pay for conversion.
Undiscovered files. Most IT teams know about the shared drives — they miss the local C:\Users folders, old laptop backups, SharePoint document libraries, and email attachments that got saved years ago. Thorough discovery is the most important first step.
If LegacyLeaps doesn't preserve your formulas, macros, and formatting, we'll refund every penny. No questions asked. Start with the free scan — see exactly what needs converting before you spend a penny.
Download Free ScannerPractical fixes for legacy Excel and Access problems. No spam.