Hi Sweta!

Before we can answer this question, I'd suggest taking the GMATPrep 1. We can't assume you're at a 640 today, as you've likely forgotten some concepts over the past year and your strategies will be super rusty. In fact, you might not even break 600! That sounds scary, I know, but we know 640 is "do-able" so it shouldn't take you too much time to get back to (and exceed) that level.

I'd suggest taking the GMATPrep 1 since it'll give you a reliable indicator of where your official score is at at this exact moment. Even if you took it 12 months ago, you likely will have forgotten all of the questions. SO do that, then email me at [email protected] and let me know how you did. How was your pacing/your ability to recall the concepts/your strategy implementation, etc. Did you finish, how long for each question, what types of problems bogged you down, etc. With more information, I could give you a much clearer assessment.

But just to generally answer your question: yes, 3-4 months is generally a reasonable amount of time for GMAT study, but you're also looking to jump 80+ points at MINIMUM (even if we're assuming you're at a 640 today). This is a serious increase, and will require a serious plan of attack. I don't think you can afford to waste time. So take the GMATPrep 1 and let me know how it goes! If you can schedule your GMAT 4 months out and commit to a minimum 20 hours a week of study (and 1 CAT a week on average), 720+ can def happen.