Partial Period Accrual - using months of service

Content

We are trying to build a Partial Period Accrual Rate fast formula to calculate the accrual in first year of service, where depending on the month of the year you join in the accrual rate is set for the first year. 

Trying something along these lines and getting error that 'a local variable was used before being initialized'

 

Can anyone advise on sample fast formula for this situation, or the variable that should be used?

 

IF (l_months > 12)

THEN

accrual = IV_ACCRUAL

ELSE
 
   if(l_months >= -1 AND l_no_of_months < 2) then
(
      accrual = 15
   )
   else if(l_months >= 2 AND l_no_of_months < 3) then