How can I structure my ordering database by a time dependent function in MySQL?

I have a table with ID and KPI like this

+----+---------------------+------------+--------+
| id | created_at          | page_views | shares |
+----+---------------------+------------+--------+
|  1 | 2015-02-25 07:24:50 |         10 |      3 |
|  2 | 2015-04-22 13:48:46 |         40 |      1 |
|  3 | 2014-09-17 15:26:51 |         28 |      5 |
|  4 | 2014-08-09 16:27:48 |        149 |      2 |
|  5 | 2015-01-21 15:56:30 |          3 |      1 |
+----+---------------------+------------+--------+

      

        
        
        
      

    

I want to create a row ranking algorithm

SELECT id FROM pages ORDER BY (pages.page_views + pages.shares * 40) / (NOW() - created_at);

      

        
        
        
      

    

But I feel it doesn't scale as the number of KPIs and inputs increases. Is there a way to structure my spreadsheet for ranking efficiently using KPIs with decreasing score over time?