Hi udit5490,
Many GMATers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, but the amount of time that YOU will need to spend will depend a great deal on your current Test-taking skills and knowledge and your overall Goal Score.
Most GMAT Companies offer some type of free materials (practice problems, Trial Accounts, videos, etc.) that you can use to 'test out' a product before you buy it, so if you want to research any courses in more detail, then there will likely be options that you can personally experience (as opposed to relying on someone else's opinions of a product). We have a variety of those resources at our website (
www.empowergmat.com). I suggest that you take advantage of all of them, then choose the one that best matches your personality, timeline and budget.
GMAT assassins aren't born, they're made,
Rich