When is Hang Seng Index Futures expiring?

The nearest expiration date for Hang Seng Index Futures is Nov 30, 1899.

When should I sell Hang Seng Index Futures?

The best time to sell a futures contract is when you've already made money on the investment, but still have plenty of time left before the expiration date. Thus, a good option would be to sell Hang Seng Index Futures before Nov 30, 1899.

What is Open interest? How can I use it to trade Hang Seng Index Futures?

Open interest is the number of contracts held by traders in active positions — they're not closed or expired. For Hang Seng Index Futures this number is 0. You can use it to track a prevailing market trend and adjust your own strategy: declining open interest for Hang Seng Index Futures shows that traders are closing their positions, which means a weakening trend.