To build on what’s already been covered, it’s worth noting that while both Interactive Brokers (IBKR) and Thinkorswim (TOS) excel in most categories, there are nuanced differences that become more apparent with advanced or institutional-style trading. For example, multiple third-party execution quality reports (such as the ones periodically published by the SEC and independent research firms) generally rank IBKR with tighter spreads and less price improvement slippage during periods of high volatility due to their SmartRouting technology, which actively seeks the best venue for each order.
For multi-leg strategies, IBKR’s commission structure can be more cost-effective for high-volume or very complex trades, especially on a per-contract basis, and they tend to have lower financing (margin) rates. However, TOS’s user interface, risk analysis tools, and options chains remain among the most comprehensive for discretionary traders or those who prioritize visualization and scenario analysis over raw cost minimization.
As for underlying breadth and liquidity, both offer access to virtually all major US options markets, but users have reported that IBKR provides superior international coverage if you’re interested in trading options on non-US exchanges.
If you’re conducting backtests or deploying systematic options strategies, TOS’s native scripting and historical data tools are intuitive, though IBKR’s API is stronger for fully automated or quantitative approaches.
Ultimately, aligning your choice with your trading style—automation and global reach vs. interface usability and educational depth—will add more value than focusing solely on headline fees or single features. If anyone has recent fill data or latency benchmarks from either platform during volatile sessions, it would help clarify execution differences even further.