create or replace function fn_get_next_monthly_date(i_in_date date) 
return date  
is  
 
    l_date date;  
    l_mb int;
begin  
     
   l_mb := months_between(sysdate, i_in_date);
     
   l_date := add_months(i_in_date, l_mb);
     
    return add_months(l_date, 1); 
 
end fn_get_next_monthly_date; 

select fn_get_next_monthly_date(to_date('25/03/1999', 'dd/mm/yyyy')) from dual

select fn_get_next_monthly_date(to_date('28/03/1999', 'dd/mm/yyyy')) from dual