Introduction

If you want to do calculations based on date cells you need to use the DATE, WEEKDAY, YEAR and MONTH functions.

Calculate second Tuesday of month

=DATE(year,month,(2*7+1)-WEEKDAY(DATE(year,month,8-DAY(dayoftheweek))))

dayoftheweek Sunday=1, Monday=2, etc

e.g. second Tuesday of June 2016

A < A function >
1 14/06/2016 =DATE(2016,6,(2*7+1)-WEEKDAY(DATE(2016,6,8-DAY(3))))

Calculate first Saturday of month using reference cells for year and month values

A B C < C function >
1 2016 06 04/06/2016 =DATE(A1,B1,(1*7+1)-WEEKDAY(DATE(A1,B1,8-DAY(7))))

Calculate first Saturday of following month using reference cells for year and month values

A B C < C function >
1 2016 06 02/07/2016 =DATE(A1,B1+1,(1*7+1)-WEEKDAY(DATE(A1,B1+1,8-DAY(7))))

Adding days, months, years

When you have a date in cell and in another reference it to add 1, Excel will by default add one day

A B < B function >
1 01/06/2016 02/06/2016 =A1+1

Because the cell number format determines how the cells actual value is presented and not the value of the cell itself, adding +1 to a cell containing simply month and year wouldn’t return following month like you might expect.

A B < B function >
1 June 2016 June 2016 =A1+1

Excel stores cell A1 as 01/06/2016 even though the cell number format applied is mmmm yyyy and therefore A1+1 = 02/06/2016 which is being displayed with same number format rule as June 2016.
To add one month use

A B < B function >
1 June 2016 July 2016 =DATE(YEAR(A1),MONTH(A1)+1,DAY(A1))

To add one year use

A B < B function >
1 June 2016 June 2017 =DATE(YEAR(A1)+1,MONTH(A1),DAY(A1))

Also see