Wow. I'm sorry you got such whiny comments. 
Thank you very much for this calculator. I had just told my husband it would be nice to build a spreadsheet to make exactly this calculation, and I guessed it was something that would have to wait until my holidays.  I expect that the people who are NOT commenting here are the people who are actually using it. 
Of *course* this is grade school math, and *of course* we don't have knowledge of the future. But many people who have busy lives  don't have the time and psychic energy at the end of a long day to build their own, not to mention remember to take into account all the different costs. So this is a godsend to me. And for those blaming the Globe for not predicting the future for them, I guess you need to lower your expectations.