Monthssinceevent

Monthssinceevent is a derived time metric used in data analysis to express the number of full calendar months that have elapsed since a specified event date for each record. It is commonly employed in cohort analysis, retention studies, and subscription metrics to quantify how long an item or individual has been in a given state since the event.

Calculation typically uses an event_date and a reference_date (often today). A common formula is: months = (ref_year - event_year) * 12 + (ref_month - event_month). If the reference_day is earlier than the event_day, one month is subtracted to count only completed months. Some implementations count calendar months and ignore days, while others use a fixed 30-day month approach, which yields a different interpretation of elapsed time.

Example: event_date = 2023-06-15 and reference_date = 2024-03-10. The raw month difference is (2024 - 2023) * 12 + (3 - 6) = 9. Since March 10 is before June 15, one month is subtracted, resulting in 8 completed months.

Applications include tracking customer tenure for churn modeling, evaluating eligibility windows for promotions or warranties, and measuring product or feature adoption over time. It is important to document the chosen rounding rule and date handling to ensure consistent reporting.

Variations and caveats: monthssinceevent can differ by calendar system (calendar months versus fixed 30-day periods), time zone and date format handling, and how incomplete months are treated. Missing event dates or dynamic reference dates can affect interpretation, so clear definitions and data quality checks are essential.