Hello,

I'm really new around here, and I'd like to believe I've searched around for to best of my ability before asking, but forgive me if this is a repeat question.

After reading through some articles I wanted to check some of the claims MMM makes about savings across 10 years myself. I've found the compound interest formula, and greatly appreciate the explanation of it at:

http://forum.mrmoneymustache.com/index.php?topic=5979.msg90112#msg90112But, as far as I can tell, this explains how a given amount,

*and only the gains from that original amount,* compound over time. Can someone explain, just as s l o w l y, how recurring expenses differ from this?

For example, in "The True Cost of Commuting" MMM claims that $19/day can add up to "about $125,000" in 10 years:

http://www.mrmoneymustache.com/2011/10/06/the-true-cost-of-commuting/I'd like to figure out how that number comes about. Because it seems like it's not just $19 compounding for 10 years. It's $19 compounding for 10 years, then another $19 compounding for 9 years and 364 days, and another $19 compounding for 9 years and 363 days, and so on, right? What's the formula for that series?