Configure Calculated Fields

Calculated fields let you compute derived values from the user’s answers. These values can be used in rules, displayed on screen, or passed to the pricing engine.

A calculated field is a formula. For example, BMI = weight divided by (height times height). You define it by listing the math operations and telling the system where each value comes from — either from a question answer or a fixed number.

How to add a calculated field

Open your questionnaire in Strapi
Scroll to the calculatedFields section
Add an entry with:
- field — The name of the computed value (e.g., bmi)
- calculation — A JSON object defining the math

Calculation structure

The calculation JSON defines a chain of operations. Each operation takes values and produces a result.

Example 1: BMI calculation

Formula: BMI = weight / (height_in_m x height_in_m)

Given questions weight (in kg) and heightInMeters (in m):

{
  "field": "bmi",
  "operations": [
    {
      "type": "DIVIDE",
      "values": [
        { "type": "dynamic", "value": "weight" },
        {
          "type": "operation",
          "operation": {
            "type": "MULTIPLY",
            "values": [
              { "type": "dynamic", "value": "heightInMeters" },
              { "type": "dynamic", "value": "heightInMeters" }
            ]
          }
        }
      ]
    }
  ]
}

{ "type": "dynamic", "value": "weight" } means “use the answer from the weight question” (from a question answer)
{ "type": "static", "value": 100 } would mean “use the fixed number 100” (a fixed number)
{ "type": "operation", ... } means “calculate this sub-formula first, then use the result”

Example 2: Annual premium from monthly price

Formula: Annual premium = monthly price x 12

Given a question monthlyPrice:

{
  "field": "annualPremium",
  "operations": [
    {
      "type": "MULTIPLY",
      "values": [
        { "type": "dynamic", "value": "monthlyPrice" },
        { "type": "static", "value": 12 }
      ]
    }
  ]
}

Here, monthlyPrice comes from a question answer, and 12 is a fixed number.

Operations

Operation	Description
`DIVIDE`	Divides value 1 by value 2
`MULTIPLY`	Multiplies all values together
`ADD`	Adds all values together
`SUBTRACT`	Subtracts value 2 from value 1

Value types

Type	Description	Example
`dynamic`	From a question answer — references a questionId	`{ "type": "dynamic", "value": "weight" }`
`static`	A fixed number that you specify	`{ "type": "static", "value": 100 }`
`operation`	A nested operation (for complex formulas)	See BMI example above

Using calculated fields in rules

Once defined, reference the calculated field’s field name as a questionId in your rules:

rule-comparison: questionId bmi, Operator greaterThan, Value 40

The rule engine evaluates the calculated field and compares the result like any other answer.