How to define rolling 12 months period?

[csh8428]

I have a data-set that looks like this

KEY_c	EFF_DT
2269_1_1	5/1/2025
2269_1_1	4/2/2025
2269_1_1	9/2/2024
2269_1_1	8/31/2024
2269_1_1	3/25/2024
2269_1_1	3/23/2024
2269_1_1	3/21/2024
5523_1_1	5/28/2025
5523_1_1	4/29/2025
5523_1_1	9/29/2024
5523_1_1	9/27/2024
5523_1_1	4/21/2024
5523_1_1	4/19/2024
5523_1_1	4/17/2024

How would I go about adding a "ROLLING_TWELVE_MONTH_PERIOD"(365 das) where the calc starts at the MIN EFF_DT for each KEY_c so the results look like this

KEY_c	EFF_DT	Twelve Month Period
2269_1_1	5/1/2025	2
2269_1_1	4/2/2025	2
2269_1_1	9/2/2024	1
2269_1_1	8/31/2024	1
2269_1_1	3/25/2024	1
2269_1_1	3/23/2024	1
2269_1_1	3/21/2024	1
5523_1_1	5/28/2025	2
5523_1_1	4/29/2025	2
5523_1_1	9/29/2024	1
5523_1_1	9/27/2024	1
5523_1_1	4/21/2024	1
5523_1_1	4/19/2024	1
5523_1_1	4/17/2024	1

[SPetrie]

Here is one method. You need to get your dates into an actual date format in order to get a time difference. Then You grab the minimum date per key and use it to compare.

I used the ceiling of the difference in days divided by 365 to get the 1 or 2 values and a formula to clean up the 0 values for same dates.