First day date in week based on particular date

public static DateTime GetFirstDayOfWeek(this DateTime date)
        {
            var dfi = DateTimeFormatInfo.CurrentInfo;
            var firstDayOfWeek = date;
            while (firstDayOfWeek.DayOfWeek != dfi.FirstDayOfWeek)
                firstDayOfWeek= firstDayOfWeek.AddDays(-1);
            return firstDayOfWeek;
        }