I guess that's up to you how accurate you want to go with your calculations. If you also want to account for inflation go for it. I didn't account for inflation because I originally did the calculation out of interest to see if I was just safe investing at 4% how much money I'd need to cover my current expenses. Once I got the number I wasn't interest in going more specific because I instantly realized it would be effectively impossible for me to make that much money. For me that number was enough to get the ballpark of what it would mean to be the ultrawealthy, I wasn't looking for a specific threshold.