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Add or Edit Custom Calculation JavaScript

Any form you create that requires calculations is likely to require custom calculation scripts. The options you have available with preset calculation formulas are limited to simple multiplication and addition. Other kind of calculation you need requires writing a script.

To write a calculation script

  1. Open the PDF in Nitro PDF Pro

  2. On the Forms ribbon, in the Form Fields group, click Text Field

    Forms Field

  3. Select the text field to edit
  4. Right-click and select Properties
  5. Click the Calculate tab
  6. Click the Custom calculation script option, and then click the Edit button
  7. Type the code for your script. In the example below, a simple routine is created to calculate sales tax at a 7.25 % rate. The code used is:
    var f = this.getField(subtotal);
    event.value = Math.round(f.value * 7.25)/100;
  8. Click OK




Last updated: June 2026

Last updated: July 30, 2026