How to decide Page Break insertion criteria in RTF doc?

Question

I am trying to develope a small RTF writer to generate project report at runtime, with a limited RTF writing capability. RTF is one page document only, untill we intentionally put page breaks in it and Project report consists of number of pages. Thus, on what criteria it should be decided to insert page break? How to keep track of page's empty area before inserting anything? Please guide.