Hello,
I have read many posts summing every nth cell. I apologize - I am still
confused as I am still somewhat of an excel novice.

I have a workbook where I track financial details for multiple projects over
the course of a year. Every 5 rows contains all the details for 1 project.

Column C Represents January, Column D Represents February etc.

In C11 I want to SUM the Forecast for all projects in January,
In D11 I want to SUM the Forecasts for all projects in February.

My project data starts at C17:
Cell C17 is the name of the Project.
Cell C18 is the Forecasted $ amount
Cell C19 is the Actual Dollar Amount
Cell C20 is the Variance (Forecast -Actuals)
Cell C21 is the EAC

All of that starts over again at C22 for my next project.

Please help - What is the formula I want to put in C11?

I have copy / pasted / modified a variey of formulas I have seen posted - I
am not getting the correct value.

Thank you so much!