what months/years/customers are in the range d4:d541?

"Deb" wrote:

I have a spreadsheet that has 29 clients information for the year 2004,
broken down by month and they've asked me to average out collections,
services provided etc. I need to have this reflect the average per month.

I first tried totalling all columns and then put basic average formula like
this in =average(d4:d541) and figured, but I'm not sure that using this
formula has given me the average per month. Would this have given me the
average per month for the entire year?

Thanks in advance for your help