Discounted Expected Value
Discounted expected value is the core concept used to bridge the gap between future uncertain payoffs and present-day value. It involves taking the probability-weighted average of all possible future outcomes and adjusting that sum to account for the time value of money using an appropriate discount rate.
In derivative pricing, this ensures that a dollar received in the future is correctly valued in terms of its worth today. The expectation is calculated over the risk-neutral probability distribution, which accounts for the market's risk appetite and ensures consistency with no-arbitrage principles.
By discounting these expected values back to the current node, the model accounts for both the uncertainty of the market and the interest that could be earned on capital over time. This calculation is the primary mechanism that drives the backward induction process in trinomial trees, allowing for the consistent pricing of complex financial instruments.