Nifty expiry is last Thursday of every month. Similarly, how does it work for MCX?
There is a fixed rule for every individual contract, for example gold the first day is the 16th of the launch month and the last day is 5th of the expiring month. But yeah it differs from one underlying commodity to the other.
You can see the entire list under contract specification in the product section of MCX website.
The question is kind of vague though, it most likely differs because each commodity in itself has multiple factors that determines the movement, unlike in the stock markets where all the stocks and Indices have a huge co-relation.
The expiry dates for commodity contracts are set considering the time & efforts required in case there is a delivery of the contract.
For e.g: The expiry of mega gold contract [1 kilo] & gold mini [100 gms] contracts are the 5th while the expiry of smaller gold contracts like gold petal [1 gm], gold guinea [8 gms] is the last day of the month. This is because to give/take delivery of the the mega contract involves higher time and effort as against giving/taking delivery of the smaller contracts of the smaller gold contracts. There are times when the gold has to be moved from Exchange’s one vault to another and moving the bigger gold denomination take longer considering the value associated with it. Similarly Silver Mega is settled on 5th while other smaller contracts of Silver are settled at the end of the month.
Most of the contracts that are cash settled expire at the end of the month.