• Junior engineer at FAANG, yr 1 = 180k ~113k take home - 42k living expenses (based off of 3.5k per month) = 71k to invest
• Yr 2 = 71k to invest
• Midlevel engineer, yr 3 = 270k ~160k take home - 42k living expenses = 118k to invest
With 10% stock appreciation per year that's roughly 78k end of 1st year, 164k 2nd year, and 310k by 3rd year.
You can live cheaper than 3.5k, sure, but that's a fairly typical amount for a single person living near FAANG office locations, if you consider rent/utilities/food/transportation/clothes/equipment expenses/entertainment.
Btw, 400k is 225k in take home, minus aforementioned living expenses is 183k. Even if you were able to get to L6 within 2 years, that's 600k the last year, 320k take home, 278k minus living expenses.
183+183+278 = 644k so you would basically need to be lucky and have 26% stock appreciation every year, which is a lot higher than the norm.