In Microsoft Dynamics CRM 2011 it is possible to pull data from a sub-grid on a parent form when a page loads to read the values.

Place the script below inside a Web Resource and call the function "calcPortfolio" on a "OnLoad" event

function calcPortfolio()
{
                var portAmount = 0.00;
                //name of the sub-grid
                var gridControl = document.getElementById("SubGridName").control;                 var ids = gridControl.get_allRecordIds();                 for(i = 0; i < ids.length; i++)                 {                                               var cellValue = gridControl.getCellValue('SubGridField', ids[i]);                                 // cellValue has a datatype of Currency
                                cellValue = parseFloat(cellValue.replace(/[$,]+/g,""));                                 portAmount = portAmount + cellValue;
               }                 var Name = Xrm.Page.data.entity.attributes.get("fieldOnParentForm");
                Name.setValue(portAmount);

}