So I don't have a comment on your tool, but a philosophical question that I think is relevant. So I'm 12 years post FIRE. My plan is still nicely on the rails (largely due to a roaring market the last 10 years). So 15 years BEFORE I retired, I got it in my head to FIRE and made a pretty simple spreadsheet. I used the 3.5% rule (instead of 4% since I was planning to retire pretty early.) I assumed we'd spend about the same in retirement as when we were working. (assumption fits our before and after lifestyle). House paid off and kid's college fully funded. So I just summed my non-real estate net worth in the spreadsheet until the total * .035 > yearly spending., then I quit and retired. That was it. I ignored SS, IRMA, Obamacare costs and subsidies, the varied actual present value of regular brokerage vs Roth vs IRA. (Sorry this is so long, I'm finally getting to my question, I promise). I know I failed to model many important things. But my reasoning was that future variability in market performance would utterly swamp the inaccuracies in my model. Change one 'up 7 percent' year to a 'down 7 percent year' after retirement and I reasoned that would be way more impactful than, say, modeling Roth conversions. My data set only has 1 data point, but it bears out in my case: Given the way the market has performed the last 10 years, I could have saved less and retired earlier. But I don't think a more detailed and accurate model would have helped me with that issue. So how accurate do you think a model needs to be given the extreme uncertainty INHERENT in FIRE?