Custom calculations in PDF forms: answered for the whole community

1 Quantity × unit price, with a grand total across all rows

    Order forms, purchase requests, invoices

Two scripts are needed. The first calculates each row's line total (quantity × price). The second, placed in the Grand Total field, sums all line totals. A loop handles any number of rows — just change one number.

Field names to use:

Paste this script in Total_1 → Calculate. For each additional row, copy the same script and change _1 to match the row number.

var qty = parseFloat(this.getField("Qty_1").value) || 0;
var price = parseFloat(this.getField("Price_1").value) || 0;
event.value = (qty * price).toFixed(2);

Paste this script in GrandTotal → Calculate. Change rows to the number of rows in your form.

var total = 0;
var rows = 5; // change to match your form
for (var i = 1; i <= rows; i++) {
  var f = this.getField("Total_" + i);
  if (f) total += parseFloat(f.value) || 0;
}
event.value = total.toFixed(2);

2 Tax amount and percentage of a subtotal

     Invoices, receipts, expense reports

Acrobat's Percentage format multiplies the stored value by 100 for display. A field showing "7%" is actually storing 0.07. To calculate tax correctly, format your tax fields as Number — not Percentage — and divide the rate by 100 in the script.
Field names to use:

The user enters the rate as a plain number — for example, 7 for 7%. Paste this in TaxAmount → Calculate.

var sub = parseFloat(this.getField("Subtotal").value) || 0;
var rate = parseFloat(this.getField("TaxRate").value) || 0;
event.value = (sub * (rate / 100)).toFixed(2);

Paste this in GrandTotal → Calculate.

var sub = parseFloat(this.getField("Subtotal").value) || 0;
var tax = parseFloat(this.getField("TaxAmount").value) || 0;
event.value = (sub + tax).toFixed(2);

3 Auto-fill today's date when the form is opened

    All form types

A custom calculation script placed in the date field reads the system clock every time any field on the form is updated, keeping the date current. The display format is set using util.printd — adjust the format string to match your region.

Field names to use:

Paste this in TodayDate → Calculate. The field's Format tab can be left as None — the script controls how the date appears.

var d = new Date();
event.value = util.printd("dd/mm/yyyy", d);
// For US format: "mm/dd/yyyy"
// For written month: "dd mmm yyyy" → 15 Jan 2025

4 Checkboxes that each add a value to a running total

    Registration forms, event booking, service selection

Set each checkbox's Export Value (in Properties → Options) to its price. The calculation script then reads all checkboxes and adds up only the ones that are checked. Unchecked checkboxes return the string "Off", not zero — the script handles this correctly. 

Field names to use:

In each checkbox's Properties → Options, set the Export Value to its price (e.g. 500, 250, 750). Paste this in CBTotal → Calculate. Change count to match your number of checkboxes.

var total = 0;
var count = 3; // number of checkboxes
for (var i = 1; i <= count; i++) {
  var cb = this.getField("CB_" + i);
  if (cb && cb.value !== "Off") {
    total += parseFloat(cb.value) || 0;
  }
}
event.value = total.toFixed(2);

5 Dropdown selection that changes what gets calculated

    Conditional pricing, membership tiers, service types

An if/else statement in the calculation script reads the dropdown's current value and runs the appropriate calculation for each option. This pattern works for Yes/No choices, multi-tier pricing, discount types, or any selection that determines how the maths should work.

Field names to use:

The string in the if statement must match the dropdown's Export Value exactly — check it in the dropdown's Properties → Options tab. Paste this in Result → Calculate.

var choice = this.getField("DDChoice").value;
var base = parseFloat(this.getField("BaseAmount").value) || 0;
var mult = parseFloat(this.getField("Multiplier").value) || 0;

6 Calculate age from a date of birth field

    Medical intake, HR, school enrolment, membership forms

The script calculates age in whole years, accounting for whether the person's birthday has occurred yet this calendar year. Using valueAsString rather than value avoids a known Acrobat issue with date fields where certain dates after May produce an incorrect raw number. 

Field names to use:

Format DOB as Date (mm/dd/yyyy) in its Format tab. Paste this in Age → Calculate.

var dob = this.getField("DOB").valueAsString;
if (dob === "") {
  event.value = "";
} else {
  var born = new Date(dob);
  var today = new Date();
  var age = today.getFullYear() - born.getFullYear();
  var m = today.getMonth() - born.getMonth();
  if (m < 0 || (m === 0 && today.getDate() < born.getDate())) {
    age--; // birthday not yet reached this year
  }
  event.value = age;

event.value = parseFloat(this.getField("FieldA").value) * 2;

event.value = (parseFloat(this.getField("FieldA").value) || 0) * 2;

this.getField("Name")

Locates a field in the PDF by its exact name.

.value

Reads the current contents of that field.

parseFloat(…) || 0

Converts the value to a number. Returns zero if the field is empty.

event.value = …

Sets the result in the field that contains the script.

.toFixed(2)

Rounds to 2 decimal places — suitable for currency and hours.

valueAsString

Safer way to read date fields. Avoids a known Acrobat date conversion issue.