What Happens When One Person Owns the Spreadsheet the Business Runs On?

Last updated: June 2026
When a single analyst builds and owns a spreadsheet the business depends on, the file quietly becomes infrastructure that nobody else can read. Research finds the large majority of business spreadsheets contain errors, and the person who built it is usually the only one who knows the logic. If they leave, the knowledge leaves with them.
A single analyst working alone on a complex business-critical spreadsheet that only they understand in 2026

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How does a personal spreadsheet become business infrastructure?

Almost no one sets out to run a department on a spreadsheet. It happens one helpful addition at a time. An analyst builds a tracker to make their own job easier. A manager asks for a tab. A second team starts sending their numbers to the same file. Two years later, the quarterly forecast, the commission run, or the production schedule depends on a workbook that grew in the dark.

By then it is infrastructure, but it was never designed as infrastructure. There is no documentation, because it was never a project. There is one author, because it was never meant to be shared. And there is a quiet assumption that the person who built it will always be around to keep it running.

How risky are the spreadsheets businesses already rely on?

More than most owners would guess, and the research on this is unusually consistent. The European Spreadsheet Risks Interest Group reports that the majority, more than 90 percent, of spreadsheets contain errors1. Field audits of real business spreadsheets have found errors across a wide span of the files examined, with the more rigorous studies landing at the higher end2.

The harder problem is psychological. People are confident in spreadsheets precisely because they do not go looking for mistakes. In controlled studies, developers estimated they had a 10 to 18 percent chance of an error, while 86 percent of them had actually made one3. The errors are not loud. They sit in a single cell, feed a total, and produce a number that looks reasonable enough to act on. A business-critical spreadsheet owned by one person is the place this risk concentrates, because no second set of eyes ever checks it.

The danger is not that the spreadsheet is wrong. It is that it can be wrong without anyone knowing, and only one person is positioned to ever find out.

What is the key-person risk, specifically?

Key-person risk is the exposure a business carries when one individual is the only one who understands how something essential works. With a spreadsheet, it shows up in a precise way. One person knows why column M subtracts a value that looks like it should be added. One person remembers the manual step every Friday that keeps the totals honest. One person can tell whether a strange result is a real signal or a known quirk.

While that person is at their desk, none of this looks like a problem. The spreadsheet works. The risk is invisible right up until the moment it is not, which tends to be a resignation, a long illness, a retirement, or a Tuesday when they are simply unreachable and a number is due. This is the spreadsheet version of a problem PCG sees across technologies, described in the IT key-man risk.

Why doesn't "just have someone else learn it" work?

It sounds like the obvious fix, and it rarely holds. The formulas are visible, but the formulas are not the knowledge. The knowledge is the unwritten context: why a rule exists, which inputs are trusted, what the owner quietly corrects before anyone sees the output, and which tabs are live versus abandoned.

A successor inherits the cells without the reasoning. They can keep the spreadsheet running on a good day, and they are lost the first time it behaves strangely, because the person who knew what strange meant is gone. Handing the file over is not the same as handing over the understanding, and the understanding was never written down.

What does moving off the personal spreadsheet look like?

The goal is to move the knowledge out of one head and into a system the whole team can rely on. The order matters, and the first step is the one that expires.

  1. Capture the owner's knowledge while they are here. Document the rules, the manual steps, and the exceptions, working with the person who knows them before that window closes.
  2. Turn the rules into a real design. The logic that lived in cells becomes enforced rules in a database, so it runs the same way every time.
  3. Rebuild it as a multi-user system. Validation at entry, a recorded history of changes, and access for more than one person, so the work no longer routes through a single desk.
  4. Keep the data with the business. The records belong to the business and move into a database the business controls, with backups and history, instead of a file on one laptop.

The data stays the business's own throughout. What changes is that the rules and the history stop being one person's private memory and become part of a system anyone authorized can run. The operational side of that change, from the point of view of the people doing the daily work, is covered in what changes when a spreadsheet moves to SQL Server.

What happens if you wait until the person leaves?

The spreadsheet keeps working after they go, which is exactly what makes waiting feel safe. Nothing breaks on the last day. The cost arrives later, when a number looks wrong and no one can explain the formula, or when a new requirement needs a change nobody dares to make.

At that point the job is reconstruction with the author gone, which is the same predicament as rebuilding software when the original developer has vanished, only now it is the spreadsheet the business runs on. PCG handles that version too, described in what to do when your developer disappears. It is solvable either way. It is simply cheaper, faster, and safer while the person who built it can still answer the phone.

Capture the knowledge before it walks out the door

PCG runs a fixed-fee discovery that documents how the spreadsheet works and quotes a path to a multi-user system with a fixed scope.

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Frequently Asked Questions

What is key-person risk in a spreadsheet?+
It is the risk that one individual is the only person who understands how a business-critical spreadsheet works. When the logic, the fixes, and the assumptions live in that person's head, the business depends on their availability, and loses the knowledge if they leave.
How common are errors in business spreadsheets?+
Research is consistent that they are common. The European Spreadsheet Risks Interest Group reports that the majority of spreadsheets contain errors, and field audits have found error rates ranging widely across the spreadsheets examined. Most go undetected because no one is looking for them.
Why can't someone else just learn the spreadsheet?+
Because most of the knowledge is undocumented. The formulas are visible, but the reasons behind them, the manual steps, and the exceptions the owner handles by habit are not written down anywhere. A successor inherits the cells without the context.
What happens if the person who owns the spreadsheet leaves?+
The business keeps running on a tool no one fully understands, until something breaks or needs to change. At that point the work of reconstructing the logic is far harder without the author present, which is why capturing it while they are still there matters.
Is a shared cloud spreadsheet enough to fix this?+
It helps with simultaneous editing, but it does not solve key-person risk. The logic still lives in one person's formulas and habits, errors are still hard to detect, and there is still no validation or audit trail. The dependency on the individual remains.
How do you move the knowledge out of one person's spreadsheet?+
By documenting how the spreadsheet works while the owner is available, then rebuilding it as a system where the rules are enforced, the history is recorded, and more than one person can run it. The knowledge moves from a person into a system the business can rely on.
Who can rebuild a business-critical spreadsheet into a real system?+
A custom software firm that does database development and legacy reconstruction. PCG has turned analyst-owned spreadsheets into multi-user systems since the late 1990s, starting by capturing the owner's knowledge before it walks out the door.
About the Author

Allison Woolbert

CEO and Senior Systems Architect, Phoenix Consultants Group

Allison Woolbert is the principal of Phoenix Consultants Group, the custom software consultancy founded in 1995. PCG has turned analyst-owned, business-critical spreadsheets into documented multi-user systems for industrial, manufacturing, and environmental services clients since the late 1990s.

Allison leads PCG's discovery and architecture practice, where the first deliverable on every engagement is a written account of how the current tool works, captured from the people who run it. LinkedIn.

1 European Spreadsheet Risks Interest Group (EuSpRIG), Research and Best Practice. The majority, more than 90 percent, of spreadsheets contain errors. eusprig.org

2 R. Panko, University of Hawaii, research on spreadsheet errors, summarized via EuSpRIG. Field audits of operational spreadsheets report error rates across a wide range of the files examined, with more rigorous methodologies at the higher end. eusprig.org; panko.shidler.hawaii.edu

3 R. Panko, spreadsheet error and overconfidence research. Developers estimated a 10 to 18 percent chance of error, while 86 percent of participants had made at least one. eusprig.org; panko.shidler.hawaii.edu

This article is informational and not legal, financial, or compliance advice for a specific situation. Phoenix Consultants Group has provided custom software development since 1995.