Excel Copilot Formula Builder in 2026: Create Any Excel Formula Using Plain English

For decades, writing Excel formulas was a skill that separated casual spreadsheet users from power users. You either knew how to nest an IF inside an INDEX-MATCH, or you spent an hour searching online. In 2026, that barrier is largely gone — thanks to Excel Copilot's Formula Builder, you can describe what you want in plain English and get a working formula in seconds.

This guide covers exactly how Excel Copilot's Formula Builder works, when to use it, and how to verify and refine the formulas it produces so you can trust them completely.

What Is Excel Copilot Formula Builder?

Excel Copilot Formula Builder is an AI-powered feature inside Microsoft 365 Excel that converts natural language descriptions into working Excel formulas. It lives in the Copilot panel on the right side of your workbook and can write formulas for cells, suggest entire columns of calculations, and explain any formula that already exists in your sheet.

Unlike older formula suggestion features (like the old formula AutoComplete), Formula Builder understands context — it reads your column headers, your data types, and what you have already built to suggest formulas that are actually relevant to your specific workbook.

How to Open Formula Builder

Open Excel with a Microsoft 365 subscription (Copilot requires Microsoft 365 Personal, Family, or a business plan with Copilot enabled).

Click the Copilot button in the Home ribbon (the sparkle icon).

The Copilot panel opens on the right side of the screen.

Click into any cell in your spreadsheet where you want a formula.

Type your request in the Copilot chat box — for example: "Calculate the average sales for the last 90 days using the Date and Revenue columns."

Copilot will suggest a formula, explain what it does, and offer to insert it directly into your selected cell.

Real-World Formula Examples

Here are practical examples of plain English requests and the formulas Excel Copilot builds from them:

Example 1: Conditional Sum

Request: "Add up all the sales in column C where the region in column B is 'North'."

Formula produced: =SUMIF(B:B,"North",C:C)

Example 2: Dynamic Lookup

Request: "Look up the employee name in column A and return their department from the HR table on Sheet2."

Formula produced: =XLOOKUP(A2,Sheet2!A:A,Sheet2!B:B,"Not found")

Example 3: Running Total

Request: "Create a running total of column D that resets to zero at the start of each month."

Copilot builds a SUMIFS-based formula that uses the Month function to check the month of each row's date and only sums rows within the same month — something that would take most users considerable time to work out manually.

Example 4: Complex Nested Formula

Request: "If the status in column E is 'Complete' and the value in column F is greater than 1000, return 'High Priority', otherwise return 'Standard'."

Formula produced: =IF(AND(E2="Complete",F2>1000),"High Priority","Standard")

Example 5: Array Formula for Unique Values

Request: "Return a unique list of all product names from column A, sorted alphabetically."

Formula produced: =SORT(UNIQUE(A2:A500))

The Explain This Formula Feature

Formula Builder is not only a creator — it is also an explainer. Click on any cell with an existing formula, open the Copilot panel, and type "Explain this formula." Copilot breaks it down in plain English, clause by clause.

This is invaluable when you inherit a workbook full of complex formulas from a colleague, or when you come back to your own work after weeks away and cannot remember what a formula was supposed to do.

How to Verify Copilot-Generated Formulas

Even in 2026, AI-generated formulas should be verified before you rely on them in critical reports. Here is a quick verification workflow:

Check the range references: Copilot sometimes uses entire column references (A:A) which can slow down large workbooks. Narrow ranges (A2:A10000) are faster.

Test with known values: Run the formula against a row where you already know the correct answer.

Ask Copilot to explain it: If you do not understand a formula, ask Copilot to explain it before using it.

Watch for absolute vs relative references: Copilot sometimes gets the $ anchoring wrong. Review whether the formula needs to be locked to a specific row or column when copied down.

Check edge cases: What happens when the lookup value does not exist? What if the cell is empty? Make sure error handling (IFERROR, IFNA) is in place.

Formula Builder vs. Copilot Column Generation

Excel Copilot offers two related but distinct features:

Formula Builder: You click into a specific cell, describe what you want, and Copilot writes the formula for that cell.

Column Generation: You describe an entire new column — for example, "Add a column that categorises each sale as Small, Medium, or Large based on the Revenue column" — and Copilot creates the column header and fills the entire column with formulas automatically.

Column Generation is faster for bulk operations, while Formula Builder gives you more precise control over individual cell logic.

Advanced Tips for Better Formula Results

Name your columns clearly: Copilot reads column headers to understand context. Headers like "Q1 Revenue (USD)" produce far better suggestions than "Col_B".

Describe the output, not the mechanism: Instead of saying "use SUMIFS", say "add up the sales where the region is North and the date is in 2026". Let Copilot choose the function.

Iterate: If the first suggestion is not quite right, refine your prompt. "Make it look at B2:B500 instead of the whole column" or "Add error handling if the lookup value is not found."

Use it for LAMBDA: Copilot can generate LAMBDA functions and help you register them as named functions in the Name Manager — dramatically accelerating custom function creation.

Conclusion

Excel Copilot Formula Builder in 2026 is not just a convenience feature — it is a fundamental shift in how people interact with spreadsheets. Whether you are a beginner writing your first SUMIF or a power user who wants to prototype a complex LAMBDA function in seconds, Formula Builder meets you where you are.

Open the Copilot panel in Excel today, describe your calculation in plain English, and see your formula appear instantly. Then spend the time you just saved on the analysis that actually matters.