10 million easily.
Through investments, 2M could produce dividends which will cover some of your basic day to day costs. Another 2M could buy you at least 2 homes that you could produce passive income when you rent them out.
That's 4 out of 10m generating money for you consistently. Another 2m for your own personal home which can be a 3 bed 2 bath with a basement. 1M can be your travel fund and the remaining money you can save for whatever comes up in the future. If you have kids, that covers their education and expenses until they're adults. With that kind of money you can get them the kind of education and networking opportunities that ensures an early retirement for them.
This is part of the reason why I say our billionaire problem is more of a health issue than a political or economic one. There are people who have access to FAR MORE than that kind of money and they feel like raising their taxes even 4 percent more is unfair. It's money that doesn't change their lifestyle at all, but their brains have been so broken by what is effectively unlimited money and they have no real problems anymore. They have to convince themselves that it's unfair for them to have 1 billion net worth instead of 2 or more billion. They need therapy, not tax cuts. It is impossible to spend 1 billion within a single life time. In the time it's taken you to read this post, Jeff bezos just made more money off his stock dividends than your entire family will make working 7 days a week, 16 hours a day at 20 bucks an hour for 100 years.