There are corn futures contracts every month, corn 170 1, corn 1702 and corn 1705. But most people only trade the contracts with the largest volume, which are also called main contracts.

The contract months that can become the main contract every year are 1, May and September.

Now the main contract is: corn 1705, and his trading volume is the largest.

When corn 1705 approaches May 20 17, the main contract is changed to corn 1709.