You may sometimes notice bids and offers showing as "0" in the market depth window. This happens in two specific situations — during the pre-open session and during Periodic Call Auction sessions. Here's why.

During the Pre-Open Session (9:00 AM – 9:15 AM)

In the pre-open session, orders are collected first and matched later at a single price, rather than being matched instantly. Market orders placed during this window don't have a fixed price attached to them — so until the opening price is discovered, they are displayed with a price of "0" in the market depth. These are known as ATO (At-the-Open) orders.

Effective September 7, 2026, the pre-open timeline has changed:

Because of this change:

• Market orders (the "0"-priced ATO orders you see in the depth) can now only be placed between 9:00 AM and 9:05 AM.
• Limit orders continue to come in until the exchange randomly closes order entry — anytime between 9:08 AM and 9:10 AM.
• Once order entry closes, matching starts right away, and the market depth updates to show the actual discovered opening price shortly after — typically by 9:12 AM.

Note for ETF traders: From September 7, 2026, Gold and Silver ETFs are included in the pre-open session for the first time. This means you will now see the same "0"-priced ATO order behavior in the market depth for Gold and Silver ETFs during the 9:00 AM – 9:05 AM window, just as you would for eligible stocks. Other ETFs (Equity, Debt, Liquid, and Overnight) do not participate in the pre-open session and continue to start trading only at 9:15 AM.

During Periodic Call Auction Sessions

The same logic applies to stocks under the Periodic Call Auction mechanism. Market orders placed during these sessions are also displayed at "0" until the equilibrium price is determined at the end of the 8-minute order matching window for that auction. Once matching completes, the depth updates to reflect the actual matched prices.

Why This Happens

A price of "0" is simply a placeholder — it tells you that the order is a market order without a fixed price yet, not that there is an actual bid or offer at zero. This keeps the price discovery process transparent and ensures all participants see the same information before final pricing is set.

Summary

• Market depth shows "0" for market (ATO) orders during pre-open and periodic call auction sessions, since these orders don't carry a fixed price until matching happens.
• From September 7, 2026, market orders in the pre-open session can only be placed in the first 5 minutes (9:00–9:05 AM), and order matching begins immediately once the exchange randomly closes limit-order entry (between 9:08–9:10 AM).
• Gold and Silver ETFs will now also show this behavior, as they join the pre-open session for the first time.
• For Periodic Call Auctions, "0" prices clear once each auction's 8-minute matching window ends.