Forty-two weeks of saving -- that means only ten weeks left!  These next ten weeks -- nearly 20% of the time spent raising this energy -- is going to account for $475, or more than a third of the total by year's end.  That's kind of like my mortgage, but in reverse.  Compound interest, working for the common good.  How about that?

It's how compounding works with money:  it adds upon itself.  When you owe a lot, like my mortgage, the interest I'm paying is based on how much I owe.  My monthly payment doesn't change, and when we started paying it was barely over the amount of interest the principle racked up in a month's time, leaving only a tiny bit to pay off the original loan, which is what the principle is.  Over time, that amount does go down, let's say by a dollar at first.  Next month, when they calculate the interest I owe, it's owed on one dollar less, so maybe I get to pay a penny less in interest, and a penny more in principle.  As the principle goes down, the amount of interest I'm paying each month drops faster and faster, until that blessed last payment, which should be pretty much all principle.

When I'm saving incrementally for this challenge, it's the money I'm stockpiling that goes up, faster and faster.  There's no interest involved (unless I put it in a bank), but the money is compounding.  If I have it in a bank, the interest payment to me would be greater every month.

Towels are incredibly useful.  So is having nearly a thousand dollars laying around.  This lesson in the magic of compound interest was brought to you by life, the universe, and everything.

My week forty-two savings: $903, 4.7% ($42) of which I added today.