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 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 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 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 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 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 average response times by month, you can use a formula based on the AVERAGEIFS function, together with the EOMONTH function.
In the example shown, the formula in G5 is:
=AVERAGEIFS(durations,dates,">=...

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 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 generate a series of dates incremented by month, you can use the SEQUENCE function together with the EDATE function or EOMONTH function. In the example shown, the formula in D5 is:
{=EDATE(B5,SEQUENCE(12,1,0))}...

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 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 count dates in the current month, you can use a formula based on the COUNTIFS or SUMPRODUCT function as explained below. In the example shown above, the formula in E7 is:
=COUNTIFS(dates,">="&...

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) //...