The Calculation of Dearness Allowance is as per the changes of AICPIN (IW) (All India Consumer Price Index Number for Industrial Workers. See how the calculation is made.
Recently all central government employees got Annual Increment which is on 01st July, 2012 and now they are getting additional Dearness Allowance with effect from July, 2012. And now this is double bonanza for them. But this happens every year, because the 6th Central Pay Commission recommended giving annual increment on July every year. The Dearness Allowance is declared twice every year from January and July.