I want to add custom tax amount to checkout cart programmatically.

Here is the example.

Cart Old Tax = 4.21

Custom Tax = 2

New Tax = 4.21 + 2 = 6

Check the screenshot below.

enter image description here

I need this done programmatically.

  • Where your custom amount come from? – Toan Nguyen Jan 10 '17 at 9:31
  • @ToanNguyen that I fetch from the session, My point is how can add that value to tax. – Dhiren Vasoya Jan 10 '17 at 9:52
  • @DhirenVasoya, below solution i tried,this is showing cart but not calculating.. – jafar pinjar May 14 '19 at 16:41
  • @DhirenVasoya - did you get the solution to this problem ? – Manashvi Birla Jul 17 '19 at 13:33
  • @DhirenVasoya, did you get solution for this/ – jafar pinjar Jun 8 '20 at 11:06

You can observe to the event sales_quote_address_collect_totals_after and achieve it. For this, you need to setup a module and configure an event. Let's say our module is MStack_Exchange.

File : app\code\MStack\Exchange\etc\events.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="sales_quote_address_collect_totals_after">
        <observer name="changeTaxTotal" instance="MStack\Exchange\Observer\ChangeTaxTotal"/>

File : app\code\MStack\Exchange\Observer\ChangeTaxTotal.php

namespace MStack\Exchange\Observer;

use \Magento\Framework\Event\ObserverInterface;
use \Magento\Framework\Event\Observer;

class ChangeTaxTotal implements ObserverInterface
    public $additionalTaxAmt = 2;

    public function execute(Observer $observer)
        /** @var Magento\Quote\Model\Quote\Address\Total */
        $total = $observer->getData('total');

        //make sure tax value exist
        if (count($total->getAppliedTaxes()) > 0) {
            $total->addTotalAmount('tax', $this->additionalTaxAmt);

        return $this;

The important call here is : $total->addTotalAmount('tax', $this->additionalTaxAmt);. This will add 2 with the existing tax amount and I think that is what you need in your case. So what you need to do is, replace $this->additionalTaxAmt with your tax buffer value.

The event sales_quote_address_collect_totals_after fires just after total calculations had been happend and hence thus become perfect place to play around.

If you are curious to know where this total calculations are happening, then you need to look into Magento\Quote\Model\Quote\TotalsCollector::collect() and Magento\Quote\Model\Quote\TotalsCollector::collectAddressTotals() methods.

  • Let me check this. – Dhiren Vasoya Feb 11 '17 at 3:04
  • @Rajeev, can we add custom tax for individual product when added to cart? here is my question,magento.stackexchange.com/questions/274520/… – jafar pinjar May 14 '19 at 11:04
  • Thanks @Rajeev to save my day – Soundararajan m Nov 14 '19 at 13:19
  • Hi @rajeev , I want to clear all taxes programmatically before adding custom tax and also want to add title of tax.Can you please let me know how to achieve it? – akgola Aug 25 '20 at 4:27
  • @akgola Hi, I am not sure which version you are referring to and feel your question is broad and cannot answer in a comment. Better ask a new question with details in the platform so that the community will help you to accomplish your need – Rajeev K Tomy Aug 25 '20 at 5:08

@Dhiren Vasoya

Use these lines as well.

$total->addBaseTotalAmount('tax', $this->additionalTaxAmt);
$total->setGrandTotal((float)$total->getGrandTotal() + $this->additionalTaxAmt);
$total->setBaseGrandTotal((float)$total->getBaseGrandTotal() + $this->additionalTaxAmt);

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