To calculate workdays per month, use the EOMONTH function together with the NETWORKDAYS function. In the example shown, the formula in C4 is:
=NETWORKDAYS(B4,EOMONTH(B4,0),holidays)
Where "holidays" is the named...

To get the last weekday in a month (i.e. the last Saturday, the last Friday, the last Monday, etc) you can use a formula based on the EOMONTH and WEEKDAY functions.
In the example shown, the formula in D5 is:
=...

To get the first day of the month for a given date, you can use a simple formula based on the DAY function. In the example shown, the formula in cell C5 is:
=B5-DAY(B5)+1
How this formula works
The DAY function...

To sum by month in columns you can use the SUMIFS function together with the EOMONTH function. In the example shown, the formula in G5 is:
=SUMIFS(amount,client,$F5,date,">="&G$4,date,"<=...

To count new customers by month, you can use a helper column and the COUNTIFS function. In the example shown, the formula in H5 is:
=COUNTIFS(new,1,date,">="&G5,date,"<="&EOMONTH(G5,0...

To check if a date is within the last n months of today's date, you can use a formula based on the AND, TODAY, and EOMONTH functions. In the example shown, we are checking for dates in the last 6 months. The formula...

To get the number of days in a given month from a date, you can use a formula based on the EOMONTH and DAY functions.
In the example shown, the formula in cell B5 is:
=DAY(EOMONTH(B5,0))
How this formula works
The...

To average by month, you can use a formula based on the AVERAGEIFS function, with help from the EOMONTH function. In the example shown, the formula in F4 is:
=AVERAGEIFS(amounts,dates,">="&F5,dates,...

To sum by month, you can use a formula based on the SUMIFS function, with help from the EOMONTH function. In the example shown, the formula in F4 is:
=SUMIFS(amount,date,">="&E4,date,"<=...

To generate a dynamic series of dates with a formula that increases by one month from a single start date, you can use a formula based on DAY, MONTH, YEAR, and DATE functions.
How the formula works
In the example, B6...

To calculate the last day of a month based on a given date, you can use the EOMONTH function. In the example shown, the formula in cell B5 is:
=EOMONTH(B5,0)
How this formula works
The 2nd argument (months) of the...

To calculate a retirement date based on a birth date, you can use the EDATE function.
In the example shown, the formula in D6 is:
=EDATE(C6,12*60)
How this formula works
The EDATE function is fully automatic, and...

To get the first day of the previous month for a given date, you can use a simple formula based on the EOMONTH function.
In the example shown, the formula in cell B5 is:
=EOMONTH(B5,-2)+1
How this formula works
The...

To get the last working day in a month, you can use the WORKDAY function together with the EOMONTH function. In the example, the formula in C4 is:
=WORKDAY(EOMONTH(B4,0)+1,-1)
How this formula works
Working from the...

To calculate an expiration in the future, you can use a variety of formulas. In the example shown, the formulas used in column D are:
=B5+30 // 30 days
=B5+90 // 90 days
=EOMONTH(B7,0) // end of month
=EDATE(B8,1) //...