When would the b-schools start, if i take up dec 18 mat exam?

Hii Swetha.. Replying in the context of fall 2019.

The deadlines for applying in Round 1 (Fall 2019 Admissions) are from September 2018 to October 2018. A good application typically requires at least 45 days of effort. Considering it’s already May now, the timeline looks really tight if you wish to apply in Round 1 itself - 45 days for GMAT Prep and 45 Days for Application Process.

Therefore, my suggestion will be to apply in the Second Round of Admissions. The deadlines for Round 2 are from December 2018 to February 2019. Note that the top B-Schools have maintained that they do not have any preference in the 2 rounds.

Hope this helps you. All the best.