Taking over an existing Excel or VBA project: what to check
By Dennis Spoelder · published 31 July 2026
A familiar situation
The freelancer or former colleague who once built the Excel or VBA file has moved on. The file still works — until, one day, it doesn't, or a change is needed that no one on the team dares to make. Macros without comments, hidden worksheets, links to files nobody can locate any more: it's one of the most common reasons organisations get in touch with an Excel specialist.
Back to topThe risks of an undocumented file
- One person in the organisation has effectively become indispensable for a business-critical process.
- Errors are only discovered after a report or calculation has already been used.
- A seemingly small change can affect hidden dependencies elsewhere in the file.
- If the one person who understands the file leaves, the process grinds to a halt entirely.
What a careful takeover looks like
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Understand before changing
First map out what the file does, which formulas and macros are active, and what external links exist — before anything is changed.
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Naming the risks
Which parts are fragile, which assumptions are hidden inside a formula, and what happens if an input is slightly different from what's expected.
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Documenting as we go
Not afterwards, but while the logic is being unpicked — so the know-how doesn't become locked up with one person again.
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Building on in a controlled way
Only once the file is properly understood do we continue development — keeping what already works well.
Why this can now be faster than it used to be
Working through a large, undocumented VBA codebase used to take weeks. With AI assistance in analysing macros and formulas, that first phase — understanding exactly what a file does — can go faster; by how much depends on the file. The thoroughness of the previous step stays: what the AI says about a file, we check before acting on it.
Back to topWondering whether your file is still future-proof?
Briefly describe what you're dealing with, and we'll explain what a takeover would involve. If we want to take a look at the file, we'll agree on a secure way to share it afterwards.