Paper Trading Fill Assumptions: A Reconciliation Checklist

Audit simulated prices, data delay, order size and fees before using a paper result to evaluate your process.

Quote and liquidity assumptions

Alpaca documents omissions around impact, queue position and latency. IBKR describes top-of-book fills and unsupported or simplified order behavior. These examples show why an instant fill is not evidence your size would execute in a real order book. Alpaca paper environment and fill limitations · IBKR paper account, API and simulator limitations

Instrument and fee settings

Check whether quantity means shares, units, lots or contracts. Specify multiplier, tick size, spread, commissions, borrow and financing where relevant. If a simulator does not model a cost, state the omission rather than interpreting it as a free trade.

Keep a reproducible test

Use one market order and one cancel/replace sequence. Record decision time, fill time, quote source, data mode and residual position. In our simple lab, every filled order records the decision date and next-open fill date; canceled and rejected requests create no fee.

Do not mix product generations

Webull’s current help distinguishes its new mobile/desktop system from legacy web. NinjaTrader playback differs from a current data connection. A product name alone cannot identify the behavior you tested. Webull new and legacy paper systems · NinjaTrader8 playback