If you are buying an option that is already "in the money" (meaning the option will immediately be in profit), its premium will have an extra cost because you can sell it immediately for a profit. On the other hand, if you have an option that is "at the money," the option is equal to the current stock price. And, as you may have guessed, an option that is "out of the money" is one that won't have additional value because it is currently not in profit.
A longer expiration is also useful because the option can retain time value, even if the stock trades below the strike price. An option’s time value decays as expiration approaches, and options buyers don’t want to watch their purchased options decline in value, potentially expiring worthless if the stock finishes below the strike price. If a trade has gone against them, they can usually still sell any time value remaining on the option — and this is more likely if the option contract is longer.
Volatility also increases the price of an option. This is because uncertainty pushes the odds of an outcome higher. If the volatility of the underlying asset increases, larger price swings increase the possibilities of substantial moves both up and down. Greater price swings will increase the chances of an event occurring. Therefore, the greater the volatility, the greater the price of the option. Options trading and volatility are intrinsically linked to each other in this way.
The price at which you agree to buy the underlying security via the option is called the "strike price," and the fee you pay for buying that option contract is called the "premium." When determining the strike price, you are betting that the asset (typically a stock) will go up or down in price. The price you are paying for that bet is the premium, which is a percentage of the value of that asset. 
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