On a small account, size every trade by a fixed dollar risk (Risk (Cents) presets of, say, $10 to $50), set the fat-finger and max-position caps below your account size, and set a daily loss limit of a few losing trades with Auto-flatten on daily loss on. Set SIM start ($) to your real balance and practise there first, and match the commission plan to your IBKR account, because fees take a bigger bite out of small trades.
Scalpel's defaults are set for a larger account: a $250,000 fat-finger cap and a $250,000 max position (there only to catch a slip of the finger), a $1,000 daily loss limit, a $25,000 SIM balance and share-count presets up to 1,000 shares. On a $5,000 account those numbers let one bad morning do lasting damage. Small accounts do not need different software; they need smaller numbers and stricter limits.
Be clear-eyed first: fast small-cap scalping carries a significant risk of loss and is very difficult, and many people who try it lose money. A small account has less room for the learning curve, so the aim of these settings is to make each mistake small and the bad days short.
Before you start
Know your account's cash and its day-trading rules at Interactive Brokers. In June 2026 FINRA replaced the US pattern day trader rule (the $25,000 minimum and the day-trade count) with intraday margin rules, but brokers may phase the change in until October 2027; check IBKR's current rules for your account type (what changed).
SIM slippage makes fills pessimistic by N cents per share (buys higher, sells lower). 0 = frictionless fills at the book price.
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Settings, Risk for a $5,000 account: SIM start, the caps and the daily loss limit with auto-flatten, outlined.
Size by risk, not by shares
A share-count button risks a different amount on every stock. With Risk (Cents), the button is the dollars you can lose and Scalpel works out the shares from your stop (guide 4.2):
Settings, Sizing: four Risk (Cents) presets from $10 to $50.
Start every session on the smallest button and earn the bigger ones with a green day, not a red one.
Caps that match the account
Max position ($) stops one symbol from growing past a set value, including adds. Keep it under your cash: SIM is a cash account and refuses orders it cannot pay for, and a live margin account will happily let you over-reach.
Fat-finger ($) caps any single order. On a small account it can equal max position.
Daily loss ($) trips the RISK LOCK when the day's realized plus open P&L reaches minus that amount: new entries are blocked until you click Resume trading. After a resume, the lock comes back only if the day's loss grows by another quarter of the limit. With Auto-flatten on daily loss on, it also closes everything (guide 7.1). $100 here is two full-size losers or three normal ones; that is the point.
Both caps block the whole order rather than shrink it, with a red toast naming the cap (guide 7.2).
Fees matter more on small trades
A 100-share trade on a $4 stock with a 20c stop risks $20. In SIM's estimate the round trip costs $1.34 on IBKR Pro Tiered (with exchange and clearing fees) and $2.00 on IBKR Pro Fixed: 7% to 10% of your risk on every trade, win or lose. Set the plan your account is really on so SIM shows you the true drag, and prefer fewer, better trades over many small ones (guide 6.3).
What to watch for
The spread eats the stop. On a 20c stop, a 6c spread is almost a third of your risk before the trade moves. Skip names whose spread is wide against your stop.
Sub-dollar stocks. Exchange fees there are a percent of value, and a cent is a large share of the price. A 20c stop on a $0.60 stock is a 33% move.
Order size resolves to zero shares. A tiny risk on a wide stop can work out to under one share. Raise the risk or tighten the stop.
Thin books. Even 250 shares can walk a pre-market ask. Watch the size line above each buy button before you press (guide 4.6).
Questions
How much should I risk per trade on a small account?
Scalpel cannot answer that for you. Many traders keep each trade's risk to a small fixed share of the account so a run of losers is survivable. Whatever you choose, set it on the buy buttons with Risk (Cents) so every trade risks the same.
Does Scalpel enforce the pattern day trader rule?
No. Interactive Brokers applies its day-trading and margin rules to your account. The pattern day trader rule was replaced by intraday margin rules in June 2026, but brokers may still be moving over, so check IBKR's current rules for your account type before you plan your week.
Can I practise with my real account size?
Yes. Set SIM start ($) in Settings > Risk to your balance and reset the SIM account. SIM is a cash account, so it also refuses orders you could not pay for.
Which IBKR commission plan is cheaper for small trades?
In SIM's estimate, IBKR Pro Tiered is cheaper than Fixed on fills under about 150 shares, because Fixed has a $1.00 minimum. Set Scalpel to whichever plan your account is on.