My first UK passport was in 1972, then 1982, then 1992, 2002, 2012 so I am on my 5th. Each time I pay extra to get a 48 page passport. That has always been enough - just. I ran my last one close. A new stamp each time into the USA plus two visas and then heavy air travel between the US and Canada can add quite a lot in a short period of time. Using BOG as a base and flying between South American countries can add a lot too. 48 pages is my best and largest.