ARS--another poster here--told me about this calculator. It's good:
It's a rough start for those that have 5+ years to go, to give them an approximate timeframe. I'd start more careful analysis once you're under 5 years.
But for a basic "how long to FIRE" question simpler is better, and in that regard it's one of the best there is.
Agreed.
In case it helps someone else just starting out, I used three calcs to get a rough picture of what my money will do over the next 5-7 years.
FIRE Calc
Investor.gov compound interest
Networthify
I've been thinking a lot about these calculators, because they are all useful.
When I first started plugging $$ into FIRE Calc, it told me I would most likely fail. It would be wonderful if this calc would provide suggestions, such as "increase savings to 40% of income, etc).
I used the investor.gov compound calc to get an idea of how my money would grow year by year assuming 5% growth, which I consider fairly conservative (but correct me if I'm wrong).
I used Networthify to get a sense of how much I need to be saving. That helped me have data for the investor.gov calc. I then plugged my revised numbers into FIRE Calc and now have a 100% chance of success.
The above is a simplified version of how I used them. I went back and forth and kept plugging away until I came up with numbers that worked out.