Start dates and end dates in C#

DateTime baseDate = DateTime.Today;

        var today = baseDate;

        var yesterday = baseDate.AddDays(-1);

        var thisWeekStart = baseDate.AddDays(-(int)baseDate.DayOfWeek);

        var thisWeekEnd = thisWeekStart.AddDays(7).AddSeconds(-1);

        var lastWeekStart = thisWeekStart.AddDays(-7);

        var lastWeekEnd = thisWeekStart.AddSeconds(-1);

        var thisMonthStart = baseDate.AddDays(1 - baseDate.Day);

        var thisMonthEnd = thisMonthStart.AddMonths(1).AddSeconds(-1);

        var lastMonthStart = thisMonthStart.AddMonths(-1);

        var lastMonthEnd = thisMonthStart.AddSeconds(-1);