The honest answer to “how much do I need” isn't a dollar figure — it's “enough to survive the variance of your strategy without being wiped out or forced to stop.” Here's how to think about it.

It depends on the instrument

Trading a single share of an ETF needs very little. Options let you start small too, since one contract can cost a modest premium — but they carry full risk of loss. Futures and pattern-day-trading rules can raise the floor. Match the instrument to the capital you actually have (the PDT rule).

The real constraint: surviving losers

Every real edge has losing streaks. If a run of losses would blow your account or scare you into quitting, you're undercapitalized for that strategy — regardless of the raw number. This is the math of risk of ruin and position sizing: risk a small fraction per trade so no streak ends you.

You're not undercapitalized when your balance is small. You're undercapitalized when a normal losing streak can end you.

Start smaller than you think

Begin with money you can afford to lose entirely, at the smallest size the strategy allows, and scale only after it's earned trust live. Starting tiny costs you almost nothing and teaches you everything — see how to start algorithmic trading and paper trading.