# Cannot override value for the calculated field with JavaScript

**URL:** <https://forum.kintone.dev/t/cannot-override-value-for-the-calculated-field-with-javascript/1742>\
**Category:** General\
**Created:** [October 19, 2026, 3:13am UTC](https://forum.kintone.dev/t/cannot-override-value-for-the-calculated-field-with-javascript/1742 "2026-10-19T03:13:42Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![rain](https://yyz1.discourse-cdn.com/flex035/user_avatar/forum.kintone.dev/rain/32/1037_2.png) [@rain](https://forum.kintone.dev/u/rain)\
**Post date:** [October 19, 2026, 3:13am UTC](https://forum.kintone.dev/t/cannot-override-value-for-the-calculated-field-with-javascript/1742/1 "2026-10-19T03:13:42Z")

</div>

## Question / Problem

I cannot override the calculated field using JavaScript.

## Current Situation

I created a Sales app that manages deals. The calculated field "total" calculates "unit\_price\*quantity". This works fine.

The app has these fields:

- Number field (unit\_price)
- Number field (quantity)
- Calculated (total, formula is unit\_price \* quantity)
- Blank space (discount\_space)

I want to add a discount feature with JavaScript. On the record add/edit screen, I placed two buttons, "10% discount" and "25% discount". When the user clicks a button, I get the record data with kintone.app.record.get(). I calculate the new "total" value, and set it back with kintone.app.record.set().

But nothing changes on the screen when the button is clicked.

### Code / Attempts

```javascript
(function() {
  'use strict';

  const events = ['app.record.create.show', 'app.record.edit.show'];

  kintone.events.on(events, function(event) {
    let spaceElement = kintone.app.record.getSpaceElement('discount_space');

    let btn10 = document.createElement('button');
    btn10.textContent = '10% discount';
    btn10.onclick = function() {
      let record = kintone.app.record.get();
      let currentTotal = Number(record.record.total.value);
      record.record.total.value = currentTotal * 0.9;
      kintone.app.record.set(record);
    };

    let btn25 = document.createElement('button');
    btn25.textContent = '25% discount';
    btn25.onclick = function() {
      let record = kintone.app.record.get();
      let currentTotal = Number(record.record.total.value);
      record.record.total.value = currentTotal * 0.75;
      kintone.app.record.set(record);
    };

    spaceElement.appendChild(btn10);
    spaceElement.appendChild(btn25);

    return event;
  });
})();

```

### Error Message

_No error message_

## Desired Outcome / Expected Behavior

The discount is applied to the Calculated value.

---

<div class="post-metadata">

**Author:** ![Chris](https://yyz1.discourse-cdn.com/flex035/user_avatar/forum.kintone.dev/chris/32/44_2.png) [@Chris](https://forum.kintone.dev/u/Chris)\
**Post date:** [October 20, 2026, 11:39pm UTC](https://forum.kintone.dev/t/cannot-override-value-for-the-calculated-field-with-javascript/1742/2 "2026-10-20T23:39:57Z")

</div>

Hello @rain

The reason your code isn't working is that **Calculated fields are read-only and their values cannot be overwritten using JavaScript customization** , including `kintone.app.record.set()`, which is documented in [the Event Object Actions documentation under the "Fields that cannot be overwritten" section](https://kintone.dev/en/docs/kintone/js-api/events/event-object-actions/).

Instead of modifying the Calculated field directly, one approach would be to add a separate Number field to manage the discount rate and include it in the calculation formula.

For example, you can try the following:

**1. Add a new Number field**

- Field code: `discount_rate`

- Default value: `0`

**2. Update the formula of your Calculated field (`total`)**

```plaintext
unit_price * quantity * (100 - discount_rate) / 100

```

**3. Modify your JavaScript to update the discount rate instead**

```javascript
(function() {
  'use strict';

  const events = ['app.record.create.show', 'app.record.edit.show'];

  kintone.events.on(events, function(event) {
    const spaceElement = kintone.app.record.getSpaceElement('discount_space');

    function addDiscountButton(label, rate) {
      const button = document.createElement('button');
      button.type = 'button';
      button.textContent = label;

      button.onclick = function() {
        const record = kintone.app.record.get();

        record.record.discount_rate.value = String(rate);

        kintone.app.record.set(record);
      };

      spaceElement.appendChild(button);
    }

    addDiscountButton('10% discount', 10);
    addDiscountButton('25% discount', 25);

    return event;
  });
})();

```

With this approach, clicking either button updates the `discount_rate` field, and Kintone automatically recalculates the `total` field based on the selected discount.

For example, if the unit price is 100 and the quantity is 5, clicking the 10% discount button changes the total from 500 to 450, while clicking the 25% discount button changes it to 375.

I hope this helps!