The case for index perps is strongest on a Saturday, when nothing else is trading. Weeknights are different. Index futures trade almost all night and they are the deeper market. So it is fair to ask what a perp adds between a Tuesday close and a Wednesday open. The answer is less than on a weekend, and a few specific things.
Futures lead on a weeknight
From Sunday evening to Friday evening, futures are the primary overnight read on the index. Globex and the overnight session covers the tape, and the Asia session and the European open cover the hours inside it. Nothing about the perp changes that order. Where the two differ on a weeknight, the deeper market gets the benefit of the doubt.
One measure, seven days a week
The first thing the perp adds is consistency. Its move is measured the same way every night: price now against its own print at the last regular cash close. Saturday’s figure and Wednesday’s figure are built identically. A trader who learns to read one can read the other, and can compare a weeknight move with a weekend move without changing instruments.
The names behind the index
The second is the mega-cap perps. Index futures give you the index. They do not break it down. The perps on the seven largest names trade around the clock, so on a weeknight you can see which of them has moved since the bell. That matters most after the close on a day when one of those companies has reported or made news.
The gaps in the futures day
The third is small and real. Futures take a short daily pause in the early evening. The perp does not pause. For that stretch the perp is the live price, the same role it plays for two whole days on a weekend.
What stays the same
The limits do not change with the day of the week. A perp has no dealer gamma, no flip and no walls. It tells you where price is on another venue. The dealer map for SPY and QQQ, as it stood at the close, tells you what that level means. And the figure is never a forecast of the next open.
Depth is still thinner than futures. A small overnight move on the perp that futures do not show is more likely to be the perp’s own book than news.
Where it shows
Trader shows the index perps’ move since the close whenever the cash market is shut, weeknights included. The push at half a percent works on weeknights too. The Perps & Futures tab carries the index perps and the mega-cap perps, with the SPY, QQQ and IWM maps alongside for the level’s meaning.