Mathematically speaking, Cost of carry (COC) is the annualized interest percentage cost for a futures contract versus a similar position in cash market and carried to maturity of the futures contract, less any dividend expected till the expiry of the contract. Imagine you had to buy a commodity and store this for future delivery for a commitment you made- wouldn’t you charge the buyer at least the interest cost for one month applied to the cost of purchasing the commodity today plus some warehousing and other incidental costs?
In pure financial derivatives like equity, warehousing etc. is irrelevant and one only treats the difference as finance costs. Note that the real-time COC values are available on stock exchange websites.
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