Custom Utility Function Equation

We have explained how to model a utility function using a map of utility points. But at times, you may want to use a custom function to define your utility function. In Rational Will, it is possible to define a custom function to reflect your utility function.

When you opened the Objective Editor for a Number type objective, you see the following buttons.

Custom Expressions button in the utility function editor that opens a free-form expression editor for defining a utility function with any supported formula.

Once you click this Custom Expressions button, you will see the following view.

Piecewise Function editor for the custom utility, listing rows of Expression F(x) with Condition (for example 0 when x less than or equal to minus 10000, 100*(1 - e^(-x/30000)) otherwise).

You can edit the expression in any way you want. You can see the corresponding chart by clicking the Charts tab.

Charts tab in the custom utility expression editor that previews the curve produced by the user-entered formula in real time.

You can learn more about the supported functions and custom expressions from this dedicated documentation page.

Last updated on Jan 7, 2026

Bernoulli Utility Function

Index Page

Certainty Equivalent Calculation