Simulations

A simulation recreates a single trading day so you can paper trade it from open to close. It's the foundation of the whole platform — the trading screen, positions, and P&L are all views into a simulation.

How a simulation works

You pick a date and a starting capital, and the system loads the historical market data for that session. Time starts at the market open (9:30 AM ET) and can be set or advanced to any point up to the 4:00 PM ET close. Every time you move the clock, the simulation recalculates everything — your positions, their Greeks, your P&L, and your buying power — from the market data at that exact moment.

Crucially, moving time is read-only. It never changes your orders or trades; it just recomputes what your account looks like at the new moment. That means you can rewind and replay as much as you like.

Historical vs live mode

The simulator runs in two parallel modes:

• Historical — any past trading day, with full control of the clock. Jump around, advance second by second, or rewind to before a trade. Covered in Historical replay.
• Live — today's session, trading against the real-time market as ticks arrive. The clock is the real clock; there's no time travel. Covered in Live trading.

Historical mode won't let you choose today's date — that's what live mode is for.

The simulation clock

A fresh historical simulation starts parked at the open with no clock set. Advancing the clock to a later time fills any pending orders whose conditions were met along the way, marks your positions to that moment, and recomputes financials. Rewinding does the reverse: orders that hadn't yet filled at the earlier time revert to pending, and trades after that time drop out of view. No data is lost — only the point in time you're looking at changes.

Account financials

At any moment a simulation reports a full financial picture, including:

• Net liquidation value — starting capital + total P&L.
• Unrealized P&L — mark-to-market gain or loss on open positions.
• Realized P&L — locked-in gain or loss from closed positions and settlements.
• Available buying power and maintenance margin — see Buying power & margin.

These are also broken down by equities vs equity options.

Per-second history

Whenever you place or cancel an order, the simulation computes a per-second history of your account financials across the whole session and stores it for charting. This is what powers the equity curve you see on the trading and positions screens.

End of day

When the clock reaches 4:00 PM ET, the session settles automatically: in-the-money options exercise or assign, out-of-the-money options expire worthless, and the results land in your realized P&L. The simulation is then marked ended. See End-of-day settlement for the details.