When volatility is not assumed to be constant, there are no closed-form solutions for the prices of European options; hence, numerical estimation is needed. In this paper, the accuracy and convergence of Monte Carlo simulation for pricing European call options under the Heston model is investigated. The empirical volatility process was characterised on the basis of the daily closing prices of the SPDR S&P 500 ETF Trust for the period January 2024 to December 2025 (502 trading days), and a standard literature parameter setting is used for the full market calibration. The paths of stock prices and variances were simulated using the Full Truncation Euler scheme with 252 time steps, while the terminal payoffs were discounted and averaged under the risk-neutral measure. These simulations were performed 20 times for 1,000, 10,000 and 100,000 paths and compared to the semi-analytical Heston price of 9.2425. As the number of paths increased, the mean standard error and the root mean square error decreased in the manner of 1/sqrt(N) rate of contraction with the relative bias being < 0.25 % throughout. The Black–Scholes special-case test was used to correctly replicate the closed-form price to within 0.073%. The estimator is thus correct at this scale but an additional discretisation error remains which cannot be eliminated by any number of additional paths.
Research Article
Open Access