Trade lasts 20 turns

[Borodin]

Q1) When trading any tips on how to dertimine when the 20 turns is over

Q2) When trading resources, it seems that the AI can cancel the deal after twenty turns. Any way for a player to cancel the deal after twenty turns or is it automatic ?

 

[Mesopotamia]

Both questions have the same answer.

Go to the Foreign Advisor screen and begin a negotiation with the Civ in question. By default, the negotiation covers 'New' negotiations. Select 'Active' (down below) instead and it'll show how many turns are remaining. What you should do is come back on Turn 0 and cancel.