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The Black-Scholes model essentially says that, if we assume some things (lognormal, constant variance, etc.) then the following the fair price of a

$$C = N(d_1) S_t - N(d_2) K e^{-rt}$$

However, another interpretation of the Black-Scholes models is that if we make the above assumptions, then we can merely pretend the drift of the underlying security is the risk-free interest rate and then interpret a derivative's expected payout as equal to its fair price.

Clearly, the lognormal assumption is required for the standard Black-Scholes formula. However, I want to know if the lognormal assumption is required for the "pretend riskless drift and then compute expected-value" perspective.

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  • $\begingroup$ @Arshdeep 's answer is in essence correct. At risk of stating the obvious I'd like to add that the asset needs to be a tradable to use $r$ as drift. If it's not tradable you can't buy/sell it and hence you don't need to fund it and hence $r$ is not required. $\endgroup$
    – Frido
    Commented Aug 3 at 7:35
  • $\begingroup$ Log-normality is not required at all for risk-neutral pricing. Models such as Heston or Bachelier assume different dynamics than the simple log-normal dynamics in the Black-Scholes model and they give the correct option prices, whilst the underlying still has to compound at riskless drift due to no-arbitrage between the spot and the forward. $\endgroup$ Commented Aug 3 at 18:42

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Not required. The result "pretend riskless drift and then compute expected-value" comes from feynman-kac, as soon as you write the condition for replication. The result is a reformulation of the fact that the delta hedged portfolio should grow at the risk free rate.

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