No offense intended to anyone but I do get a chuckle when I read about the lengths people go to trying to 'calculate' when their FIRE date will be.
I FIREd 26 years ago. The term FIRE didn't even exist I don't think. If it did, I'd certainly not heard of it. Bear in mind the birth of the World Wide Web was only 26 years ago. Research meant a library and books. I did none of that. I just decided one day that I did not want to work till I was 65, retire and then drop deap on the golf course at age 67. So I invented if you will, the idea of FIRE for myself.
So I sat down one evening and came up with a 10 year plan to retirement. Here's how I figured it out. I figured(I didn't need to 'calculate', I just pulled what I felt was a reasonable number out of the air) that I needed $20k or so of passive income based on a conservative average of around 10-12% ROI (this is back in 1982) per year to start out with. I believed I could actually live quite happily on as little as $12k a year. So $20k would allow me plenty of wiggle room and the ability to continue building capital over time. I was earning around $35k a year and owned my home. I would need to have $200k capital at 10% to return the $20k income I wanted. If I wanted to get there in 10 years I needed to save around $20k per year. That was my entire plan, took about an hour of thinking.
Then I set out to reach the goal of $200k. It was clear to me that it would be a bit tough on $35k per year income unless I was going to give up things and I had no intention of doing that so it was also clear that I needed to increase my income. That meant that instead of just 'coasting' in my job and doing an average job I needed to up my game and outperform my peers in order to make more income. I went from $35k to $100K in 5 years. At no time did I do without vacations or steak dinners or anything else. In fact, truth be told, I increased my spending somewhat during those years. Nevertheless, I spent less than I earned and in fact reached my 10 year goal in 7 years.
So you could say I pretty much planned it all on the back of an envelope and pretty did everything most people here would tell you not to do. I'm also pretty sure, any 'retirement calculation program' would show I had no chance of retiring successfully when I did. The only problem with that is that I retired 26 years ago and am still retired with an income that is now going to be $65k per year (as a couple) when a pension kicks in this summer.
All calculations are based on assumptions as MDM says. I call that crystal ball thinking. A decision to retire which is an emotional decision, comes first. Then comes 'how much do I need'. You make a guesstimate. Yes, that's right, a guesstimate, because unless you have a crystal ball, you have no way of knowing what the future will bring. Any 'calculator' like 'firecalc' et al are no better at guessing than you are.
So going back to your question, 'how did you figure out your fire date?', the answer is when I guesstimated I had enough. So far, so good and that is really all anyone can hope for.
