A while ago I wrote a spreadsheet to help a client understand that if he bought a Bugaboo on his credit card he'd still be paying for it when the child started University
here it is
docs.google.com/spreadsheet/ccc?key=0AiZqlQ7-gn07dHRoTXA5Qnlld25UWkw1TEhZZk9IYVE&authkey=CMjc4JEB&authkey=CMjc4JEB#gid=0
And then on a thread this evening, somebody asked about how to explain the risks of an interest only mortgage
so I wrote this
docs.google.com/spreadsheet/ccc?key=0AiZqlQ7-gn07dDN4clg5OXhLMGJWbHZhOEo4UTJINEE#gid=0
Enter your figures into the highlighted boxes and the sheets do the rest ....
I check them every few weeks and correct any glitches ...