Less than you think — and the amount matters far less than the habits. What actually determines whether you get anywhere.
The most common beginner blocker is “I don't have enough to start.” The honest answer: you can start with very little, and the starting amount is one of the least important variables. This is general education, not financial advice.
Fractional shares and low-cost funds mean you can begin with a modest amount — the point of starting isn't the size, it's building the habit and learning how you react when numbers move.
Consistency (adding regularly beats timing a lump sum), costs (fees and spreads quietly compound against you), time (the earlier you start, the more compounding does the work), and not risking money you need soon. A small amount invested consistently for years beats a big amount invested once and panic-sold.
Never invest money you can't afford to lose or will need in the near term. Markets fall, sometimes hard; money you might need next month has no business in stocks.
When you do put money to work, size each position so a loss can't sink you — that's position sizing, and it matters more than the account balance.