The first thing to do is take a diagnostic test from GMATPrep and mimic test conditions as much as possible. This will tell you where you stand. If you consider your score respectable, then by all means go for it!
Another thing to consider is that GMAT burnout sets in usually around the sixth month. I have come across a few accounts of people studying for one year and then performing poorly on the test. And at that point it's nearly impossible for these individuals to rebound and retake. Mentally and emotionally drained, they simply have no energy left. This is a very real possibility for anyone who overextends their studies.
Another problem is that with a "one year" mentality, you may become lackadaisical and passive about your studies. You need to be determined, focused, and energized. Very few can do so for a whole year.
I'm leaning toward the October plan. Also, you will probably start to wind down your GMAT preparation during the last two weeks, so you can balance work and study at the same time. In other words, I think that you could extend your study schedule to early November and be fine.
But, in the end, it all depends on you. Whichever path you choose, here are some books and other resources that you will need for a top score:1. QUANT:
All five Manhattan math books.2. VERBAL: Powerscore CR
, Manhattan SC.3. QUESTIONS OG Verbal
, OG Quant
, OG 12th
Edition, GMATClub Tests
.4. PRACTICE TESTS:
GMATPrep, Manhattan online tests.
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