There are many pagerank prediction tools out there, yet non of these tools does the job correctly or even work. They are not based on true information and every prediction website has their own way of calculating or guessing your next PR.

Your website pagerank depends on many factors such as incoming links and outgoing links from your website. Keep in mind that the quality of these links is also another important factor, because getting a backlink from a pagerank 9 website is not the same as getting a backlink from a pagerank 3 website !

Pagerank prediction tools such as iwebtool, simply ignore most of these factors and predict your future pagerank according to how many backlinks you have in google. keeping in mind that google does not show the true number of your website backlinks due to competition issues !

Seochat and Live PR tools are not pagerank prediction tools but they were called so, to attract more users and visitors. These tools simply check's your website pagerank on google datacentres and that's it !

If you get the pagerank directly from a datacentre then that's the PR that datacentre has for your website - it's not a prediction, that's what it is ! You might see different pagerank on different datacentres but that's during a pagerank update while the new pagerank propagate around all the datacentres.

Anyway, I personally recommend you stop wasting your time on prediction tools and start working more, on the quality of your website content and backlinks.