Prompt - Cohort and Retention Analysis Explainer

Prompt - Excel/Sheets Formula Builder

Act as a spreadsheet expert. I need a formula in [Excel/Google Sheets] that [DESCRIBE WHAT YOU WANT]. My data is laid out as: [DESCRIBE COLUMNS/RANGE]. Give me the exact formula, explain what each part does, show a worked example, and offer one alternative approach (e.g. a pivot table or a cleaner formula) if it's better. Warn me about common errors like circular references or off-by-one ranges.