How to Calculate User Retention Cohorts from CSV Data with Python

How to Calculate User Retention Cohorts from CSV Data with Python Manually calculating retention cohorts in Excel takes hours and leaves you drowning in formulas that break every time your data changes. When your user base grows beyond a few hundred accounts, the manual approach becomes unsustainable, and expensive BI tools aren't always an option for smaller teams. The Manual Way (And Why It Breaks) Most developers start by exporting user signup data and activity logs into separate CSV files, then importing them into Excel. They create pivot tables to group users by signup week, manually calculate retention percentages for each cohort period, and apply conditional formatting to visualize trends. Every time new data arrives, they repeat the entire process. One typo in a formula can corrupt an entire cohort calculation, and scaling beyond monthly retention means copying complex formulas across dozens of columns. The spreadsheet becomes a maintenance nightmare when you need to adjust dat