I can really see the power of saving and compounding, and I hope this trend continues until we FIRE.
Congratulations on that milestone! I remember hitting $400K, and it definitely felt like a big deal to me! And, with saving and compounding, I think you'll find those $100K intervals will get shorter and shorter.
I've been keeping track of my progress, and the intervals went something like this:
0-100K: 71 months (recovered from a bad divorce, bought a brand-new car, phased out a second job, tech burst and 9/11 tragedy were all in this timeframe)
100K-200K: 16 months (sold a condo, so that helped a bit)
200K-300K: 16 months
300K-400K: 12 months
400K-500K: 28 months (the Great Recession caused some problems there)
500K-600K: 10 months
600K-700K: 14 months (2011 was a flat year for me)
700K-800K: 13 months
800K-900K: 8 months.
As I mentioned earlier, I started paying down my mortgage, so if I hadn't done that, I would have hit $900K sooner, and possibly even $1M by now. But, early in 2013, if my investable assets hit a new month-end high, then the beginning of the following month, I'd cash out $10K and use it to pay down the mortgage. I did this five times, total. I think I did it a couple times before I broke $800K, and a few times after. I'm sure that if I hadn't taken that $50K, plus potential gains off the table, I'd be over the $1M mark by now.
Keep up the good work, and let us know when $500K comes around!