This is a simple example with three input parameters and one calculated output.
It uses a third-party plugin for the slider interface: Cf7 UI slider. The same result can be achieved with standard number fields.
Source code for this form:
<label> Loan amount ($)
<br>
[cf7_ui_slider loan_amount id:loan_amount min:0 ui_default:5000 max:10000 step:100] </label>
<label> Yearly interest rate (%)
[number rate min:0 max:100] </label>
<label> Months to pay
<br>
[cf7_ui_slider months id:months min:1 ui_default:6 max:24] </label>
[calculate_button calculate_button-1 "Calculate"]
<label> Monthly payment:
[calculation payment min:0 precision:2 "loan_amount * (1+rate/12*0.01)^months*rate/12*0.01 / ((1+rate/12*0.01)^months - 1)"] </label>