Thank you for the response. I am afraid that my question was not clear. Some additional data may help:
I am 64 and intend to wait until I reach FRA in June 2021 to file.
My wife is 64 and plans on retiring in June 2020. Her FRA is December 2021.
We were married in January 2020.
If she files for her benefit upon retirement (17 months before FRA), the benefit based on her work record would be [PIA-Wife * (100-5/9*17)/100]. When I reach FRA she will meet the two criteria for spousal benefit (length of marriage and spouse is receiving benefit). Her spousal benefit would then be [(PIA-Husband/2-PIA-Wife)]*(100-25/36*MONTHS)*2/100].
The question I was trying to ask is whether MONTHS is equal to 17 (based on date she intends to file) or 6 (based on date she becomes qualified for the spousal benefit).
Any spousal benefits for which your wife qualifies would be reduced based on the number of months that she starts drawing the spousal benefits prior to her full retirement age (FRA). So, if she starts drawing spousal benefits 6 months prior to FRA, her spousal rate would be reduced by 6 x 25/36ths of 1%. That's true even if she starts drawing reduced Social Security retirement benefits before then.