var employees = ctx.Employees.Where(d => d.BirthDay.Month == 5 && d.BirthDay.Day >= 11 && d.BirthDay.Day <= 18);

DateTime dateStart = DateTime.Today;
int incDays = 7;

int monthStart = dateStart.Month;
int dayStart = dateStart.Day;

int monthEnd = dateStart.AddDays(incDays).Month;
int dayEnd = dateStart.AddDays(incDays).Day;

var employees = ctx.Employees.Where(d => 
    (d.BirthDay.Month == monthStart && d.BirthDay.Day >= dayStart) || 
    (d.BirthDay.Month == monthEnd  && d.BirthDay.Day <= dayEnd)
);

declare @d1 as datetime
declare @d2 as datetime

set @d1 = '20110321 00:00:00'
set @d2 = '20110327 23:59:59'

select FullName, new_dob
from Contact
where cast(datediff(dd, new_dob, @d1) / 365.25 as int) - cast(datediff(dd, new_dob, @d2) / 365.25 as int) <> 0
order by new_dob

int monthSpan = (dateEnd.Year - dateStart.Year) * 12 + dateEnd.Month - dateStart.Month;

int days = 7;
var now = DateTime.Today;

var employees = from emp in ctx.Employees
                let thisYearsBirthday = emp.BirthDay.AddYears(now.Year - emp.BirthDay.Year) 
                let nextBirthday = (thisYearsBirthday >= now) ? thisYearsBirthday : thisYearsBirthday.AddYears(1)
                where nextBirthday >= now && nextBirthday < now.AddDays(days)
                select emp;