Well, the general impression is that Kaplan scores tend to be a bit lower than actual GMAT scores. You can see this discussed here:

https://www.beatthegmat.com/books.html

I personally believe that Kaplan tests are not necessarily harder, but more academically oriented, so to speak. Kaplan focuses on the straightforward math problems, while the GMAT also hits hard with some pretty nasty word problems. It all depends on your general taste for different problems.

My own personal experience with test scores is as follows: the free test is greatly skewed in quant. I got only three mistakes but still scored way below what I was supposed to get (can't remember if it was 46 or 48), since something like three days later I took another Kaplan test, had three mistakes but scored 53... While most of my scores in Kaplan were around 740, I did also get 800 on one test, which kind of made my day... But again, it's a personal view.

GMAT Prep is the correct indicator... you can relay on it.. It will indicate where you stand. Everyone here accepts it. Do a GMAT Prep and decide.

crejoc, what you said about GMATPREP, is that true even if we repeat it many times? My verbal score in GMAT prep reached from 25 to 40 in 3 weeks times, I have taken these test atleast 10 times (5 times each) in this duration. Now, I am wondering where do I stand in verbal. Only one week is left for my GMAT exam, I don't know what should I do now to get an idea of my verbal abilities.

Any suggestions?

Taking GMATprep twice and sometimes three times does not skew your score. However, I'm pretty sure that taking it 5 times will likely result in higher scores than normal for your last two attempts.

As Dana mentioned , it may skew your scores after 5 or more times as the questions gets repeated.. You must have kept one test untouched for evaluation in the last week of your prep, because both the tests have different bin of questions, But everyone follows different study plan. Do the free MGMAT(Manhattan Gmat) test online, they say it has a tolerance of +/- 30 points of the real indication of your score, and most agree with it.