Modern models are much better than they were, but they still make arithmetic and logic slips, especially with long chains of numbers. Asking them to show working makes errors visible.

Should I trust the recalculated values?

Use them to find problems, then confirm in a spreadsheet or calculator. The value is in spotting which figures need a second look.

Can it check spreadsheets?

Paste the relevant cells or upload the file if your AI supports files. It works best when inputs and outputs are both included.

Check the Numbers: AI Prompt to Verify Calculations

The skill#

Check the numbersMeticulous financial analyst checking someone else's numbers

Act as a meticulous financial analyst checking someone else's numbers.

Here is the material: [PASTE TEXT, TABLE OR CALCULATION]

1. List every number, percentage, total and comparison in it.
2. Recalculate each one from the inputs given, showing your working.
3. Check that percentages, growth rates and totals are consistent with each other.
4. Flag figures that cannot be recalculated from the inputs provided.
5. Flag numbers that are implausible for the context, and say why.

Do not round until the final step. Do not assume any figure is correct.

Return a table:
Figure | Stated value | Recalculated value | Match? | Note

How to use it#

Copy the skill into any capable AI model.
Paste the text, table or calculation in place of the bracketed field. Include the raw inputs where you can.
Re-run any figure it flags in a spreadsheet before you use it.

Example#

Paste a pitch-deck slide saying revenue grew from $1.2M to $1.8M, "a 60% increase". The table shows the correct growth is 50%, and flags a margin figure that cannot be recalculated from the numbers given.

Quick and strict versions#

Use the quick version for everyday checks and the strict version when the result matters.

Quick version

Recalculate every number in this text and list only the ones that are wrong or cannot be checked, with the correct value and your working.

Text: [PASTE TEXT]

Strict versionAuditor

Act as an auditor. Material: [PASTE TEXT, TABLE OR CALCULATION]

1. Extract every figure and the inputs it depends on.
2. Recalculate each one twice using two different methods (for example forward and reverse calculation), showing both.
3. Check units, currencies, time periods and whether like is compared with like.
4. Check percentage changes use the right base, and that totals equal the sum of their parts.
5. Flag anything that relies on a number not given in the material.

Do not round until the end. If a calculation is ambiguous, state each interpretation and its result.

Return: Figure | Stated | Method 1 | Method 2 | Status | Issue

Use it as an agent skill#

Save this as SKILL.md in a folder named after the skill, and agents that support skills (Claude, Claude Code and other skill-aware agents) can load it automatically when the task fits.

markdown

---
name: check-the-numbers
description: Use when the user shares a document, spreadsheet summary or analysis with numbers and wants the calculations checked.
---

# Check the numbers

Fill each [BRACKETED] field from the conversation. If one is missing, ask the user for it before starting.

Act as a meticulous financial analyst checking someone else's numbers.

Here is the material: [PASTE TEXT, TABLE OR CALCULATION]

1. List every number, percentage, total and comparison in it.
2. Recalculate each one from the inputs given, showing your working.
3. Check that percentages, growth rates and totals are consistent with each other.
4. Flag figures that cannot be recalculated from the inputs provided.
5. Flag numbers that are implausible for the context, and say why.

Do not round until the final step. Do not assume any figure is correct.

Return a table:
Figure | Stated value | Recalculated value | Match? | Note