Financial Anchor Numbers Worth Memorising

Estimation questions in a markets interview often want a finance-specific reference point rather than a general-knowledge one, and having a handful memorized cold saves precious minutes of reasoning from scratch. A useful starter set: total US stock market capitalization ≈ $50 trillion, S&P 500 average daily trading volume ≈ $400-500 billion, US GDP ≈ $27 trillion, total US household debt ≈ $17-18 trillion, and a typical large-cap stock's daily dollar volume ≈ $100 million-$1 billion depending on the name.

These don't need to be precise to the dollar — they need to be close enough in order of magnitude that a chain of reasoning built on top of them lands in a defensible range.

A worked example

"Estimate total daily trading volume across all US equities." Anchor from total US market cap ($50 trillion) and assume something like 0.3-0.5% of market cap turns over per day on average (a reasonable turnover anchor from index-level daily volume figures), giving roughly $150-250 billion per day. The actual figure across all US exchanges is typically $400-600 billion including all listed names beyond just the S&P 500, so this estimate is in the right order of magnitude even if it undershoots by roughly half — good enough to demonstrate sound reasoning under interview time pressure.