Paper Trading¶

OVERVIEW¶

Paper trading is simulated trading. You enter orders the same way you would on a live broker, the orders fill against simulated market conditions, and you track P&L without real money on the line. Done right, it's a learning environment where execution mistakes are cheap and behavioral habits get built. Done wrong, it's a video game that teaches you to expect fills you'll never get live.

Most retail paper-trading platforms do it wrong. This is not an opinion. It's a statement about what their fill engines actually model and what they don't.

Note

Most retail paper-trading platforms fill at mid-price, skip regulatory halt enforcement, and charge no borrow on shorts. Tapeboard enforces all three. The engine is harder by design.

WHAT "WRONG" LOOKS LIKE¶

The most common shortcut retail paper platforms take is filling at mid-price. A market order to buy 1,000 shares of a stock with a bid of $42.10 and an ask of $42.14 fills the paper trader at $42.12 — the midpoint. The next click goes to mark-to-market and the trade looks instantly profitable by half the spread.

In live markets, that's not what happens. Your market buy hits the ask at $42.14. If the ask only had 500 shares available, the next 500 fill at $42.15 or higher as the order walks the book. You're starting the trade at the bottom of a small but real hole — the bid-ask spread plus any size impact — and the live broker rightfully shows it. The paper-trading platform that fills at mid hid this from you, and after 200 paper trades you've trained your brain to expect entry quality that doesn't exist.

The second common shortcut is no enforcement of regulatory halts. SSR (Reg SHO Rule 201, the uptick rule that triggers when a stock drops 10% from prior close) and LULD (Limit Up / Limit Down volatility halts) are two of the most common regulatory events a US-equity day trader runs into live. Paper platforms that don't enforce them let you short freely on a -15% day, let you trade through a 5-minute halt, and let your alerts fire on prices that wouldn't have been touchable in reality. You learn that the trade was easy. The next time it happens live, you discover that it isn't.

The third common shortcut is no borrow cost on shorts. Real shorts pay a daily carry equal to position value times the annualized borrow rate, divided by 365. Hard-to-borrow names — exactly the names retail short-squeeze traders are drawn to — can carry annualized fees of 50%, 200%, sometimes more. A 1,000-share short of a $4 stock at 150% borrow accrues over $16/day in carry, independent of whether the trade is profitable. Paper platforms that don't model borrow let you sit on a short for two weeks for free. You learn that you can wait shorts out. Live, you can't.

WHAT "RIGHT" LOOKS LIKE¶

Realistic paper trading models the three shortcuts above directly.

Fill Engine¶

Orders walk the L2 order book rather than filling at mid-price.

A market buy hits the best ask. If the best ask doesn't have the size you wanted, the rest of the order consumes the next level, and the next, until the share count is satisfied. The reported fill price is the volume-weighted average of the levels consumed. Partial fills happen when book depth is genuinely thinner than the requested size — and the paper engine returns the partial rather than topping you up at a price that doesn't exist.

Scenario	Retail Platform (typical)	Tapeboard
Market buy, full size available at ask	Fills at mid	Fills at ask
Market buy, partial size at ask	Fills at mid for full size	Walks book; VWAP of levels consumed
Size exceeds available depth	Fills at mid for full size	Returns partial fill

See Tapeboard's L2 walk-book methodology for the full specification.

Regulatory Halt Enforcement¶

SSR (Reg SHO Rule 201) and LULD (Limit Up / Limit Down) are enforced server-side.

When a stock drops 10% from prior close, SSR flips on and the paper engine refuses short fills below the last consolidated print. When a stock's 5-min VWAP band breaks, the paper engine halts trading for 5 minutes and resting limit orders sit until resume. The rejection codes match what a live broker returns, so the paper trader learns the same defensive habits they'll need on the real account.

Event	Trigger	Paper Engine Behavior
SSR	Stock drops ≥ 10% from prior close	Short fills below the last consolidated print are rejected
LULD halt	5-min VWAP band breach	Trading halted for 5 minutes; resting limit orders held until resume

See Tapeboard's SSR + LULD methodology for full enforcement logic.

Tip

Use SSR and LULD rejections in paper as practice. If the engine rejects your order, the same order would have been rejected live. Adjust your entry strategy before it costs real capital.

Short Borrow Carry¶

Every paper short position accrues a daily borrow cost. Hard-to-borrow names cost what they cost. Easy-to-borrow names pay the median. Either way, the paper trader feels the cost of holding a short and adjusts their hold-time expectations accordingly.

Variable	Source
Annualized borrow rate	Published IBKR rate per symbol
Daily charge	`(Position value × annualized rate) ÷ 365`
Rate tier	Hard-to-borrow names use actual HTB rate; easy-to-borrow names use median rate

Example: A 1,000-share short of a $4.00 stock at 150% annualized borrow accrues $16.44/day in carry, regardless of P&L on the position.

See Tapeboard's short borrow methodology for the full daily mark-to-market calculation.

The combined effect is that a paper trader who hits 50 profitable trades on a realistic engine has a much better chance of those skills surviving the transition to live trading than a paper trader who hit 200 profitable trades on a mid-price engine. The realistic engine is harder. That's the point.

WHY RETAIL PLATFORMS TAKE THE SHORTCUTS¶

The shortcuts are computationally cheaper and emotionally more flattering. Mid-price fills don't require a live L2 book in the simulator — the platform doesn't need to subscribe to depth-of-book data for every paper account. SSR and LULD enforcement require server-side state tracking per symbol. Borrow rate carry requires nightly ingestion from a stock-loan feed and a daily mark-to-market routine on every open short position.

All three are real engineering work. A paper-trading product that's competing on user growth has the incentive to skip them, because users who lose less in paper feel better about the product.

HOW TO USE¶

Open the Paper Trading tab from the main terminal navigation.
Select an account type: Margin or Cash. Borrow charges apply to margin accounts only.
Enter an order using the standard order entry panel. All order types available on the live terminal are available in paper.
Review the fill confirmation. The confirmation displays:
Fill price (VWAP across book levels consumed)
Number of shares filled vs. requested
Any regulatory rejection code if the order was blocked
Monitor open short positions in the Positions panel. The Borrow Cost Today column updates each trading day at market close.
Review cumulative P&L in the Paper P&L report, which nets borrow carry against realized and unrealized gains.

Note

Paper account data resets are available once per calendar month. Navigate to Settings → Paper Account → Reset to clear positions and P&L history.

KEYBOARD SHORTCUTS¶

Shortcut	Action
`P`	Toggle paper trading mode on / off
`Shift + B`	Open buy order entry (paper)
`Shift + S`	Open sell / short order entry (paper)
`Shift + C`	Cancel all open paper orders
`Shift + F`	View fill history for current session
`Shift + R`	Open paper account reset dialog
`Esc`	Dismiss order entry panel