Computer Columns performance

I have to deal with a few poorly designed tables that instead of capturing an instance (say a record for each record on a patient) they have fields called xray1, xray2,xray3, etc) upto six fields. These tables might contain at max 2-3000 records per year. One of the summary reports they want against these tables is a sum of counts (like add the number of xray1,xray2, etc fields) . I was wondering if for speed purposed if I came up with a calculation to count these occurances at the table level using a computed column. Is there a performance degradation using computed columns. Any input appreciated