Looking for Sum formula based on a condition

[sandhya16]

i have a column containing 1 to 36 representing months(A2:A37) and i have one more cell(M1) in which i am calculating the month by taking difference between two dates.

So i want a formula that match M1 with A2:A37 value and based on match i want to add the column values(B2:B37) corresponding to match.

for eg. -if M1= 5 ,i want to get the sum from B7:B37 and so on depending on M1 value. if the value of M1 =0 then i want to sum from B2:B47.

Please help.

 

[Jonmo1]

Try

=SUM(INDEX(B2:B37,M1+1):B37)

 

[sandhya16]

Actually i am looking for formula to add from the starting ..sorry for the confusion

if M1=8 then add from B2 to B29 and if M1=0 add from B2 to B37..how to do that?

 

[Jonmo1]

Maybe

=SUM(B2:INDEX(B2:B37,36-M1))