Excel is officially a programming language: Here’s what that means

If you thought Microsoft Excel was just for data entry, think again. It has evolved into an officially Turing-complete programming language, a milestone that turns the grid into a functional programming environment. Here’s why that changes everything for you.

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What is Turing completeness?

The Alan Turing statue at the University of Surrey.

In computer science, Turing completeness is the gold standard for power. Named after the World War II code-breaker Alan Turing, it refers to any system that, given enough time and memory, can solve any computational problem that a “real” computer can.

For decades, Excel was essentially a sophisticated calculator, where advanced logic required fragile, nested workarounds. You could add numbers, find averages, or look up data, but you were limited by the functions Microsoft gave you. If a formula didn’t exist for the job you wanted to do, you reached a dead end or had to write complex scripts in VBA.

By becoming Turing complete, Excel’s native formula language has moved from a limited tool to a universal one, meaning the formula bar is now a language capable of the same logic as Python, Java, or C++. While I’d advise against wasting time building a 16-bit CPU in Excel, the mathematical reality is that you could. This shift signifies that the walls of what you can build in a spreadsheet have officially been torn down. If you can dream up an algorithm, Excel now has the logical infrastructure to execute it.

The LAMBDA function changed everything

If Turing completeness is the engine, LAMBDA is the steering wheel. While Excel could simulate Turing machines via cumbersome formulas for decades, this single function bridged the gap between writing a formula and writing software. Historically, formulas were trapped within the cell where they were written, meaning if you created a brilliant piece of logic to calculate a specific tax bracket, you had to copy and paste that massive string of text every time you wanted to use it.

LAMBDA lets you define, name, and store your own custom functions, introducing the concept of abstraction to Excel. You can take a complex, thirty-line calculation and collapse it into a single, readable name like Calculate_Risk(), and once defined, you call it just like you would =SUM or =XLOOKUP.

Excel's Name Manager defines a custom function named EXTRACT_EMAIL using a complex LAMBDA and LET formula.

This shift turned the formula bar into a true development environment, allowing for modularity—where you can build a library of custom tools that work across your entire workbook. By giving us the power to create our own vocabulary, Microsoft gave us the key to building our own mini-programs within the grid.

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Using recursion to solve any problem

In traditional programming, recursion is a technique in which a function calls itself to solve a smaller part of a larger problem. For a long time, this was notoriously difficult to achieve in Excel—a formula that referenced its own cell would trigger a circular reference error, causing the spreadsheet to throw up its hands in confusion.

However, LAMBDA now handles recursion properly with named, self-calling functions. Think of it like a set of Russian nesting dolls: the function opens one doll, finds another inside, and repeats the process until it reaches the center.

The Name Manager in Excel defining a recursive function called REVERSE_TEXT. The spreadsheet grid shows column A with words like "EXCEL" and "TURING," while column B shows those words successfully reversed using the custom =REVERSE_TEXT(A1) formula, demonstrating functional recursion within the spreadsheet.

This capability is what allows Excel to handle highly complex data structures. Whether you’re trying to navigate a complex corporate hierarchy, parse a long string of messy text, or calculate interest across a fluctuating timeline, recursion allows the formula to keep working until the logic is satisfied.

Don’t worry about infinite loops crashing your PC—Excel has built-in limits on how many times a formula can call itself to keep things stable.

As a result, it’s no longer about a single calculation—it’s about a sequence of logical steps that can run as long as necessary to find the answer.

Dynamic arrays and the “infinite” grid

While LAMBDA provides the logic, dynamic arrays provide the space. In the old Excel, a single formula lived in a single cell. If you wanted to see a list of results, you had to manually drag the fill handle down the column. This was static, brittle, and prone to human error.

Modern Excel uses spill behavior—denoted by a thin blue border around the calculated range—meaning one single formula can return a whole range of data that dynamically resizes based on the result. If your formula finds 10 items, it fills 10 cells, and if the data grows to 100 items tomorrow, the resultant range automatically spills to accommodate them.

The UNIQUE function in Excel producing a spilled range of product names from a table.

This transforms the spreadsheet from a static ledger into a reactive environment. It behaves less like a paper grid and more like a modern app interface where the UI (the cells) automatically adjusts to the underlying data. When combined with Turing-complete logic, this means you can build programs that generate their own tables, reports, and dashboards on the fly. The grid is a flexible canvas that grows and shrinks as your code executes.

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Why Turing completeness matters to you

You might wonder why Turing completeness is more than just a fun Excel fact for computer scientists. The real-world benefit comes down to portability and security.

As I said earlier, historically, if you wanted to build advanced logic into a spreadsheet, you had to use VBA macros. This created two major headaches. First, macros are a notorious security risk. Indeed, in 2022, Microsoft changed the default behavior of Office apps to automatically block VBA macros in files downloaded from the internet, and many IT departments block XLSM files to prevent malware. Second, since VBA is old tech, it struggles to work with others, including Excel for the web and the Excel mobile app.

Because Excel’s new programming power is baked directly into the formula language, your complex programs now live in standard, safe XLSX files. They work seamlessly in a browser, on an iPad, or shared via Teams without triggering security warnings.

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This shift democratizes development. You don’t need to learn a separate coding language or get permission from IT to install specialized tools—if you have access to a cell, you have access to a full-scale programming environment. It allows you to build robust, app-like tools that are natively compatible with the modern, cloud-based way we work today.

With Excel becoming a Turing-complete language, you no longer need to step outside the grid or learn a secondary language to build complex, automated systems. While it won’t replace dedicated programming for massive applications, it turns the spreadsheet into a powerful low-code platform. However, with this new power comes the need for better organization. Just as a software engineer documents their scripts, you should start documenting your Excel formulas like code to ensure your logic remains readable for anyone else using the sheet.