More than likely, this is because cFIREsim and FireCalc calculate bond returns differently (thus, you'll see this difference get bigger the larger percentage of bonds you have). This change is documented here: http://www.cfiresim.com/phpbb/viewtopic.php?f=2&t=119 I did a lot of discussing with folks on bogleheads to come to this conclusion.
A while ago when I was trying to figure out why Trinity, Pfau, FIRECalc, and cFIREsim all gave different SWRs. I figured it was something to do with using different data sources (and likely the bond sources in particular), but then I was surprised that I couldn't find anything describing the actual data sources used for cFIREsim, even after reading the whole cFIREsim FAQ (not that the other research is terribly forthcoming either). I guess I should have asked, and even now, should probably be posting this at the cFIREsim forums, but this is my lazy way of saying: add this to the FAQ! Even just that link to the forum would be better than nothing (I believe I also quickly browsed the forum but didn't find that thread).
Anyway, this topic also goes along with my "why do we trust who we trust" musings. It's funny how even today, all we see during discussions of SWR are references to "Bengen" or "The Trinity Study". That shit is
old news. It has been far-surpassed by the Trinity-style flexible simulation-engines of FIRECalc and cFIREsim, and now we see that cFIREsim has gone even further and found and corrected what I see as a major error/omission in those original works.
But still, we'll continue to reference that hoary old research. Why? Because the guys that did that hoary old research had fancy letters before or after their names, and wrote their stuff in a serif font on two-columned dead-tree paper (now PDFs) rather than on the wild-and-crazy World Wide Web. It's just dumb how a forum like this is filled with people every bit as smart or even smarter than those guys, who have done as much or more work and research and insight-creation, and we fail to recognize that. So this is me trying to recognize it. Awesome work, bo_knows! (and NW-Bound at the e-r.org forums)
Bengen and The Trinity Study should no longer be mentioned by anyone, except as the creators of the (very valuable) prior work to cFIREsim.
It was also interesting how the NW-Bound thread came out of analyzing the Y2K retiree, and thus, there seemed to a belief that incorporating price-changes into bonds would
raise the SWR. But after programming it into cFIREsim, we see that, although it did raise the returns for that Y2K retiree, it actually
lowered the SWR. Just more evidence of how hard it is to grasp/remember that SWR is a worst-case number, not an average-case number!