By John Summa, CTA, PhD, Founder of OptionsNerd.com
An essential element determining the level of option prices, volatility is a measure of the rate and magnitude of the change of prices (up or down) of the underlying. If volatility is high, the premium on the option will be relatively high, and vice versa. Once you have a measure of statistical volatility (SV) for any underlying, you can plug the value into a standard options pricing model and calculate the fair market value of an option.
Volatility changes can have a potential impact  good or bad  on any options trade you are preparing to implement. In addition to this socalled Vega risk/reward, this part of the options volatility tutorial will teach you about the relationship between historical volatility (also known as statistical, or SV) and implied volatility (IV), including how they are calculated, although most trading platforms provide this for you.
In this tutorial, we'll look at what is meant by historical volatility and implied volatility, which is then used to determine whether options are expensive (meaning are they trading at prices high relative to past levels) or cheap. Also, we'll look at the question of whether options are overvalued or undervalued, which pertains to theoretical prices versus market prices and how historical and implied volatility are incorporated into the story.
Most options traders  from beginner to expert  are familiar with the BlackScholes model of option pricing developed by Fisher Black and Myron Scholes in 1973. To calculate what is deemed a fair market value for any option, the model incorporates a number of variables, which include time to expiration, historical volatility and strike price. Many option traders, however, rarely assess the market value of an option before establishing a position. (For background reading, see Understanding Option Pricing.)
This has always been a curious phenomenon, because these same traders would hardly approach buying a home or a car without looking at the fair market price of these assets. This behavior seems to result from the trader's perception that an option can explode in value if the underlying makes the intended move. Unfortunately, this kind of perception overlooks the need for value analysis. Too often, greed and haste prevent traders from making a more careful assessment.
Perhaps the most practical aspect of a volatility perspective on options strategies and option prices is the opportunity it affords you to determine relative valuation of options. Due to the nature of markets, options may often price in events that are expected. Therefore, when looking at option prices and considering certain strategies, knowing whether options are "expensive" or "cheap" can provide very useful information about whether you should be selling options or buying them. Obviously, the old adage of buy low, sell high applies as much here as it does in the world of stocks and commodities.
Another important use of volatility analysis is in the selection of strategies. Every option strategy has an associated Greek value known as Vega, or position Vega. Therefore, as implied volatility levels change, there will be an impact on the strategy performance. Positive Vega strategies (like long puts, backspreads and long strangles/straddles) do best when implied volatility levels rise. Negative Vega strategies (like short options, ratio spreads and short strangles/ straddles) do best when implied volatility is falling. Clearly, knowing where implied volatility levels are and where they are likely to go once in a trade can make all the difference in the outcome of strategy. But you first have to know what Vega is and how to interpret it before you can put it to good use. (For more on these strategies, see the Option Spread Strategies tutorial.)
Finally, we'll look at uses of options volatility in relation to vertical and horizontal skews, where the implied volatility levels of each strike are compared in the same expiration month (vertical) and across different months (horizontal). This is followed by a look using implied volatility as a predictor of the future direction of stocks and stock indexes. Implied volatility can be used as a predictor of price from two angles: as a contrarian, when implied volatility has moved too far  high or low  or as a sign of potentially explosive price moves when implied volatility is extremely high for no apparent reason. Typically, the latter occurs when there is a pending unknown or even known event but it is not clear which way the stock will move. All that the extremely high implied volatility tells you is that something big is in the offing.
In all parts of the tutorial, we'll provide key insights and practical tips about how to use the concepts mentioned above as they relate to volatility and Vega.In the meantime, spend some more time reading and studying about volatility than trying to trade  you will not be disappointed. Good luck!
Option Volatility: Historical Volatility

Trading
Implied Volatility: Buy Low and Sell High
This value is an essential ingredient in the option pricing recipe. 
Trading
What is Meant by Implied Volatility?
The estimated volatility of a security's price. 
Trading
Stock Options: What's Price Got To Do With It?
A thorough understanding of risk is essential in options trading. So is knowing the factors that affect option price. 
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The Anatomy of Options
Find out how you can use the "Greeks" to guide your options trading strategy and help balance your portfolio. 
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Option PriceVolatility Relationship: Avoiding Negative Surprises
Learn about the pricevolatility dynamic and its dual effect on option positions. 
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Ratio Writing: A HighVolatility Options Strategy
Selling a greater number of options than you buy profits from a decline back to average levels of implied volatility. 
Investing
The Volatility Surface Explained
Learn about stock options and the "volatility surface," and discover why it is an important concept in stock options pricing and trading.