# Describe a calculation, get a formula

> Describe the calculation you want in plain words and AI writes the formula for the cell you are on, explains it, and adds any columns or tabs it needs.

Source: https://plexiidesk.com/help/sheets-ai-formula
Section: Office > PlexiiSheets
Plans: All plans
Updated: 2026-10-15

You do not need to know a function's name to use it. Click **AI** beside the formula bar, say what you want to work out, such as "gross margin: revenue minus cost, divided by revenue", and AI proposes the formula for the cell you are on, with a sentence explaining it. You see the formula before anything is written.

## Before you start

- **Plans.** AI formulas are on every plan.
- **AI needs to be set up:** PlexiDesk credits while you are signed in, or your own Anthropic key. See [AI credits and where your AI runs](https://plexiidesk.com/help/ai-credits).
- **Name your columns** if you can, such as Revenue and Cost. AI reads the column names and the first few rows to understand your data.

## Get a formula

1. Click the cell where the answer should go.
2. Click **AI** beside the formula bar. The **AI · Write a formula** panel opens above the grid.
3. Describe the calculation in the box. It suggests what to write for the cell you are on.
4. To refer to a column exactly, click its button under the box, such as **B: Revenue**. The button for the cell you are on, such as **D2**, adds its reference too.
5. Click **Suggest formula**, or press `⌘` `Enter` on a Mac (`Ctrl` `Enter` on Windows). The button reads **Thinking…** while AI works.
6. Read the formula and the explanation under it.
7. Click **Apply** to write it into the cell, or **Re-suggest** for another.

The formula goes into the cell you were on, and calculates straight away. Applying it is one step, so one undo takes it back.

## When AI needs more room

Sometimes the calculation needs a column or a tab that is not there yet, such as a Margin column. The preview then lists them under **Applying will also create**:

- **Columns:** added at the right of the sheet, with their names.
- **Tab:** added at the end of the sheet tabs, with a note of what it is for.

They are only created when you click **Apply**.

## What AI will and will not write

- AI only offers a formula PlexiiSheets can calculate. If it suggests one that cannot be read, you see a message asking you to describe the calculation differently, and nothing is written.
- The result is a real formula, so it recalculates when your figures change, and shows an error value if something is wrong, rather than a made-up number.

## Write better descriptions

- **Name the columns.** "Revenue minus Cost for this row" is clearer than "the profit".
- **Say the shape of the answer.** "As a percent", "rounded to two decimals", "only for rows where Status is Done".
- **Say the range** if it is not the whole column: "the average of the first ten rows".

## Close the panel

Click the **×** at the top right of the panel, or click **AI** beside the formula bar again.

## Common questions

**The formula refers to the wrong cells.**
Click **Re-suggest**, or change your description to name the columns. You can also edit the formula after applying it. See [Formulas, functions and named ranges](https://plexiidesk.com/help/sheets-formulas-and-functions).

**I want to fill a whole column with the formula.**
Apply it to the first cell, then drag the small square at the cell's corner down, or double-click it. See [Fill, copy and paste](https://plexiidesk.com/help/sheets-fill-copy-paste).

**The panel says no API key is set.**
AI is not set up yet. Sign in to use PlexiDesk credits, or add your own Anthropic key. See [AI settings](https://plexiidesk.com/help/settings-ai).

## Related tasks

- [Formulas, functions and named ranges](https://plexiidesk.com/help/sheets-formulas-and-functions)
- [Build a sheet with AI fill](https://plexiidesk.com/help/sheets-ai-fill)
- [Insights and questions about your sheet](https://plexiidesk.com/help/sheets-assistant-insights)
- [AI in PlexiiOffice](https://plexiidesk.com/help/office-ai-actions)
- [AI settings](https://plexiidesk.com/help/settings-ai)