Glossary
What is AUM (Assets Under Management)?
Updated Reviewed quarterly
AUM stands for Assets Under Management — the total dollar value of a fund. SPY (the world's largest ETF) has over US$550B in AUM. A small ETF might have under US$100M. AUM matters because larger funds usually have tighter bid-ask spreads, better liquidity, and lower closure risk.
For long-term buy-and-hold investors, AUM matters mostly as a survival signal. Funds with under US$50M in AUM occasionally close (forcing you to realise gains and find a replacement); large funds (over US$1B) rarely do. For active traders, AUM affects bid-ask spreads — a tight 1-cent spread on SPY (huge AUM) vs a 5–10-cent spread on a thin small-cap ETF can swallow returns over many trades.
Where you’ll see this term