Yes, that's generally the math. You save 80% of your income while learning to structure your life to live on the 20%. These people bike everywhere, eat cheaply, and are all around frugal. If you can do that, then in 5 years you can retire and have to worry less about money. For me personally, that would mean sacrifices to my family's lives that I'm not willing to make, but I see the appeal and try to apply the concepts where I can.

If you want more than the 20, you just need to save a bigger stack.

In general, you just need to plug in your target income from your investment, and your expected long-term return in percent. That gives you the amount of money you need to save.

The more you save per year, and the lower your target income, the faster you get there.

You can also do some consulting projects here and there to get a big boost for that year. I'm living in a expensive place and have kids so it's not really doable for at least some years for me