Margin and cash accounts, in plain terms.

A cash account

You trade with money that has settled in the account. A sale settles the next business day, and until it does the proceeds are not spendable again. No borrowing, no shorting. If you buy with unsettled money and sell before it settles, the broker calls it a good-faith violation and, after a few, restricts the account.

• Buying power = your settled cash.
• Shorts are refused — the broker's rule, and Atheneo says so before the order goes.
• Henry on a cash account is long-only, whatever the plan says.

A margin account

The broker lends against what you hold. You can buy more than your cash, you can sell short, and you owe interest on what you borrow overnight. The broker sets a maintenance level; fall below it and you get a call to add money or close positions.

• Overnight buying power is what you can hold past the close.
• Day-trading buying power is usually higher and resets each morning. Not every broker reports it over its API; where one doesn't, Atheneo shows a dash and says why instead of repeating the overnight figure.
• Shorts are allowed; Henry still never holds one overnight.

Paper is margin

Your paper account is a margin account with a 2× multiplier, so you can practise shorting and sizing against buying power before you do it with real money.

The pattern day trader rule

The old $25,000 rule for day trading on margin was retired in 2026. Your broker's own limits still apply, and Atheneo reads them from the broker rather than assuming.