We were getting contradicting information about Airtel's data carry forward from different customer care representatives. So we decided to try it out on our own, to help our users as well as Airtel customer care representatives.  

Many customer care represent said data will carry forward only to next immediate cycle. But today we can see that it is not true. Whole of the data (previous + current) from previous cycle got into the new cycle. 

Even a degrading plan change was doe in the cycle.