Abstract: Methods and apparatus provide for calculating expected present values and conditional probabilities of future payments of path-dependent rules-based securities or derivative contracts using iterative conditional probability calculation methods, including: (a) breaking a payment horizon of the securities or derivative contracts into N time increments over time t=0 to t=N; (b) initializing an array of state variables to assumed values at t=0; (c) applying transition probability models to the assumed values of the state variables at time t=0 and calculating a joint probability distribution for the state variables at time t=1; (d) applying payment calculation models to both the t=0 and t=1 values of the state variables and calculating probabilities and expected present values for the securities or derivative contracts payments occurring between t=0 and t=1 based on values of the state variables at times t=0 and t=1; (e) repeating steps (c)-(d) iteratively at each time t and calculating joint probability distribut