One line extra on some pages, can't work out how to make even. HELP!

Hey guys, I'm trying to write a novel through Word, but more often than not I cannot get the bottom lines of each page to match up, E.G. 24 lines on one page, and 23 on the next, even if the paragraph continues over to the next page. If I do manage to make them even,  the last word on the page falls out of allignment with the last word of every sentence above it.

If my query makes sense, can anyone advise how to make sure every page remains even in terms of line number?