If this then that formula

I am trying to figure out a formula that if P2 is >=1000 add 120 days to the date in M2 in cell O2, if P2 is <=999 add 90 days to the date in M2 in cell O2. I cannot seem to get it to return a correct answer. Any help is greatly appreciated.

=SUMIFS(M2,P2,">=1000",M2,120,P2,"<999",M2,90)

I'm 100% sure my formula is not even close.