Factors Affecting Option Value

Updated for the 2026-2027 CFA® Level I curriculum.

An option's value depends on six factors: the underlying price, the exercise price, time to expiration, volatility, the risk-free rate, and any income paid by the underlying. Each factor pushes call and put values in specific, sometimes opposite, directions. Level I tests whether you can identify each factor and state its directional effect correctly, without confusing calls and puts.

Key Takeaways About Factors Affecting Option Value

• Six factors determine option value: underlying price, exercise price, time to expiration, volatility, risk-free rate, and income on the underlying.

• Underlying price and call value move together. Underlying price and put value move apart.

• Exercise price works in reverse: higher exercise price lowers call value and raises put value.

• Volatility raises the value of both calls and puts because it increases upside potential without changing downside risk beyond the premium paid.

• More time to expiration usually raises value for both American calls and puts, but a longer-dated European put can be worth less than a shorter-dated one in some cases.

• A higher risk-free rate raises call value and lowers put value, holding other factors constant.

• Income paid by the underlying, such as dividends, lowers call value and raises put value.

What You Need to Know for CFA Level I

• Identify each of the six value factors by name and know which apply to the underlying versus the contract terms.

• State the directional effect of each factor on calls and separately on puts.

• Recognize that volatility increases value for both calls and puts, not just calls.

• Distinguish the time-to-expiration effect for American options from the more limited effect on European puts.

• Apply "holding other factors constant" reasoning when a question changes only one variable.

• Avoid confusing exercise price effects with underlying price effects. They move in opposite directions from each other.

What Determines Option Value?

An option's value comes from the relationship between the underlying asset and the contract terms, combined with the passage of time and market uncertainty. Six factors matter at Level I:

1. Underlying price

2. Exercise price

3. Time to expiration

4. Volatility

5. Risk-free rate

6. Income or carrying benefits on the underlying

Each factor is examined by changing it alone and holding the rest constant. This is the standard approach the exam uses, and it is the approach this note follows.

Underlying Price

A call option gives the right to buy at the exercise price. When the underlying price rises, that right becomes more valuable. Call value increases as underlying price increases.

A put option gives the right to sell at the exercise price. When the underlying price rises, the right to sell at a fixed, now relatively lower, price becomes less valuable. Put value decreases as underlying price increases.

This is the most intuitive factor and also the one most often reversed under exam pressure. Calls move with the underlying. Puts move against it.

Exercise Price

The exercise price is fixed in the contract, but comparing it across two otherwise identical options shows its effect.

A call with a lower exercise price is more valuable, because the holder can buy at a better price. A call with a higher exercise price is less valuable. So call value decreases as exercise price increases.

A put with a higher exercise price is more valuable, because the holder can sell at a better price. So put value increases as exercise price increases.

Exercise price and underlying price move option value in opposite directions from each other for a given option type. That contrast is a common exam setup.

Time to Expiration

More time to expiration generally means more value for American options, both calls and puts. Extra time means more opportunities for the underlying price to move favorably, and the holder is never forced to exercise early.

European options are different in one specific case. A European put does not always gain value from extra time. Because early exercise is not allowed, a longer-dated European put can sometimes be worth less than a shorter-dated one, particularly for deep in-the-money puts, since the holder must wait longer to realize the exercise value's present worth.

At Level I, the safe general rule is: more time raises value for American calls, American puts, and European calls. European puts are the exception worth remembering.

Volatility

Volatility measures how much the underlying price is expected to fluctuate. Higher volatility raises the value of both calls and puts.

This works because option payoffs are asymmetric. A call holder benefits from large upward moves but loses only the premium on downward moves. A put holder benefits from large downward moves but loses only the premium on upward moves. Higher volatility increases the chance of a large favorable move for both option types without increasing the maximum loss beyond the premium already paid.

A common misconception treats volatility as helpful only to calls. It raises value for both.

Risk-Free Rate

The risk-free rate affects the present value of the exercise price the option holder will pay or receive.

For a call, a higher risk-free rate lowers the present value of the exercise price the holder will eventually pay, which raises call value. For a put, a higher risk-free rate lowers the present value of the exercise price the holder will eventually receive, which lowers put value.

So a higher risk-free rate raises call value and lowers put value, holding other factors constant.

Income and Carrying Benefits

Dividends or other income paid by the underlying asset reduce the underlying's price over time relative to a no-income scenario. This works against call holders and in favor of put holders.

Higher expected income from the underlying lowers call value and raises put value. This mirrors the risk-free rate pattern but comes from a different mechanism: cash leaving the underlying asset rather than time value of money on the exercise price.

Call vs Put Directional Effects

The table below summarizes the direction of effect for each factor, holding all other factors constant.

Worked Example

Setup: A stock trades at $50. Consider a European call and a European put, each with an exercise price of $50 and six months to expiration. Assume no dividends for the base case.

Scenario 1: Stock Price Rises

The stock price rises to $55, all else unchanged. Predict the direction before reading on.

The call becomes more valuable because the right to buy at $50 is now more attractive when the stock is at $55. The put becomes less valuable because the right to sell at $50 is less attractive when the stock is worth more than the exercise price.

Scenario 2: Volatility Rises

Instead of the stock price change, assume volatility rises from 20% to 35%, all else back to the original $50 stock price.

Both the call and the put increase in value. Higher volatility raises the chance of a large price swing in either direction, and both option types benefit from the increased chance of a favorable outcome without added downside beyond the premium.

Scenario 3: Dividend Yield Is Introduced

Instead of volatility, assume the stock begins paying a dividend equivalent to 3% annually, all else at original levels.

The call value decreases and the put value increases. The dividend reduces the expected growth path of the stock price, which works against the call holder and in favor of the put holder.

Plain-English interpretation: each factor has its own separate directional effect. Testing one change at a time, with the others held constant, is exactly how Level I questions isolate the concept.

Common Exam Traps

• Reversing the underlying price effect on puts. Candidates often apply the call logic to puts by habit. Remember that put value moves opposite to the underlying price.

• Assuming more time always helps every option. This is true for American options and European calls, but some European puts can lose value from additional time. Do not apply the American-option rule automatically to every European put scenario.

• Believing volatility only benefits calls. Volatility raises value for both calls and puts because the payoff structure is asymmetric on both sides. If a question implies volatility change hurts one option type, check the logic.

• Mixing exercise price effects with underlying price effects. These two factors move option value in opposite directions from each other for the same option type. A rising exercise price is not the same as a rising underlying price, and the effects are reversed.

Practice Questions

An analyst compares two otherwise identical European put options on the same stock. Put A has an exercise price of $40. Put B has an exercise price of $45. All other contract terms and market conditions are identical.

Which statement is correct?

1. Put A is worth more than Put B because a lower exercise price always increases option value.

2. Put B is worth more than Put A because a higher exercise price increases the value of a put.

3. Put A and Put B have equal value because exercise price does not affect put value.

FAQs About Factors Affecting Option Value