How to calucate percentage

<!--- percentage to decimal accuracy --->
<!--- <cfset percentCollected = 100*350/2300>
<cfset percentDue = 100*1950/2300> --->

<!--- rounded percentage --->
<cfset percentCollected = round(100*350/2300)>
<cfset percentDue = round(100*1950/2300)>

<!--- pie chart (as image or flash) --->
<cfchart format="png"> 
<!--- <cfchart format="flash">  --->
<cfchartseries type="pie">
<cfchartdata item="Collected" value="#percentCollected#">
    <cfchartdata item="Due" value="#percentDue#">
</cfchartseries>
</cfchart>

You can use cfchart to do this.  Here are a few tutorials on its use http://www.quackit.com/coldfusion/tutorial/coldfusion_charts.cfm

Or just use jquery, as really you don't need ColdFusion to do this necessarily.

http://xaviershay.github.com/tufte-graph/

<cfoutput>#(350/2300)*100#</cfoutput>

That is the usual mathmetical way to calculate a percentateg.

How you plan to display that may be another issue.