I have a rental income spreadsheet where COLUMN C is 2011 income and COLUMN D is 2010 income. Totals for 2011 and 2010 can be found in cell C23 and D23 respectfully.

I need a formula that would be able to show if only one year is completed (EITHER year), then the subtotal must = that year’s value found in either C23 or D23 and have it displayed in cell C25. If BOTH years are completed, then the subtotal must be the average of C23 and D23 and displayed in cell C25.

I currently have in cell C25:
=IF(D23>=1,(C23+D23)/2,C23)


Any help would be GREATLY appreciated.