UPDATING A COLUMN BY CALCULATING BASED ON PREVIOUS ROW

I have problem in updating a column based on previous row.
Consider i have following Table.
NetPensionTable
SNO     BPS   YEAR NetPension
1    21      2010     
2         21      2011
3         21      2012
3         21      2013
and so on
I have to update NetPension column based on year , e.g in year 2010 i have calculate NetPension 5000 , i have to calculate 2011 NetPension based on previous column i-e 2010 Pension.
Kindly help me in such regard.
Thanks in advance