NAVに対するプレミアム・ディスカウント
ETFの市場価格とNAV（純資産価値）の乖離と、その発生理由。
An ETF trades at a premium when its market price is above its NAV and at a discount when below. The percentage gap is (price − NAV) ÷ NAV. For most large U.S.-equity ETFs the gap stays within a few basis points because authorized participants profit from closing it.
Persistent premiums or discounts appear where arbitrage is harder: funds holding foreign securities (time-zone mismatch), bond funds during stressed markets (stale bond quotes), or funds with capped creations. A discount is not automatically a bargain, and a premium is not proof of quality; both mainly reflect pricing friction.
Practical takeaway: check the typical premium/discount behavior of a fund, and be careful trading in the first and last minutes of the session or when the underlying market is closed.