Options, Put-Call Parity, and Binomial Pricing

How Level I tests option payoffs, moneyness, time value, value drivers, put-call parity, and one-period option pricing logic.

Options are where many Level I candidates either gain easy points or lose them fast. The exam usually starts with payoff classification, then moves to moneyness and value drivers, and finally tests whether you understand how arbitrage links calls, puts, stock, and cash.

Why This Lesson Matters

Candidates often miss options questions because they:

  • confuse payoff with profit
  • mix long and short positions
  • forget that moneyness and time value are different ideas
  • memorize put-call parity without understanding the replicated payoff

The stronger reader draws the payoff in words before calculating anything.

Option Payoff And Option Profit Are Not The Same

For a call option at expiration:

$$ \text{Call payoff} = \max(S_T - X, 0) $$

For a put option at expiration:

$$ \text{Put payoff} = \max(X - S_T, 0) $$

Profit for the option buyer adjusts for the premium paid. That is why a positive payoff does not automatically mean a positive profit.

Long And Short Positions Reverse The Economic Exposure

PositionWhat you want
Long callUnderlying price to rise
Short callUnderlying price to stay below or not rise too much above exercise price
Long putUnderlying price to fall
Short putUnderlying price to stay above or not fall too much below exercise price

Level I frequently tests position direction before anything more advanced.

Exercise Value, Moneyness, And Time Value Answer Different Questions

ConceptMeaningCommon trap
Exercise value (intrinsic value)Immediate economic gain from exerciseTreating it as the full option value before expiration
MoneynessWhether the option is in, at, or out of the moneyConfusing it with profitability after premium
Time valueOption value beyond current exercise valueForgetting it falls as expiration approaches, all else equal

A call is in the money when (S > X). A put is in the money when (S < X).

Option Values Respond Predictably To Key Inputs

FactorCall value effectPut value effect
Higher underlying priceIncreasesDecreases
Higher exercise priceDecreasesIncreases
Higher volatilityUsually increasesUsually increases
Longer time to expirationUsually increasesUsually increases
Higher interest ratesUsually increasesUsually decreases

These relationships are a favorite Level I testing pattern because they reward understanding over memorization.

Put-Call Parity Comes From Equivalent Payoffs

For a European call and put on a non-dividend-paying stock with the same strike and expiration:

$$ C + \frac{X}{(1+r)^T} = P + S_0 $$

The equation matters because the two sides create equivalent expiration payoffs. If the pricing relationship breaks, arbitrage may exist.

One-Period Binomial Pricing Uses The Same No-Arbitrage Logic

In a one-period binomial model:

$$ C_0 = \frac{pC_u + (1-p)C_d}{1+r} $$

with risk-neutral probability

$$ p = \frac{(1+r)-d}{u-d} $$

The deeper point is that contingent claim pricing can be built from replicated payoffs and no-arbitrage, not only from intuition about expected price moves.

How CFA-Style Questions Usually Test This

  • by asking for payoff or profit from long or short calls and puts
  • by testing moneyness and time value separately
  • by asking how one factor changes an option’s value
  • by using put-call parity or a one-period binomial setup to check pricing consistency

Mini-Case

A candidate sees a call that is in the money and concludes the long holder must have a profit. That is incomplete. A stronger answer asks whether the intrinsic value exceeds the premium originally paid.

That is standard Level I design: payoff logic first, profit logic second.

Common Traps

  • confusing intrinsic value with profit
  • reversing long and short exposures
  • assuming volatility helps calls but hurts puts
  • using put-call parity without checking that strike and expiration match

Sample CFA-Style Question

Which change is most likely to increase the value of both a call option and a put option on the same underlying?

Best answer: Higher expected volatility, because optionality becomes more valuable when the range of possible outcomes widens.

Why: Level I likes value-driver questions because they reveal whether you understand the economics of optionality.

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