We are currently implementing the Dots/FastTax plugin to extend from the initial Mage_Tax_Model_Calculation class. By doing so, we are able to provide a dynamic tax rate for both cart estimate tax quote and actual checkout.

The issue, however, is that tax is currently showing on an initial session. In other words, when a user adds an item to the cart and proceeds to checkout cart, you can see a default tax amount. This default tax amount usually is estimated to 8% of the total item cost.


The plugin is responsible for one key method extension, that is the calcTaxAmount:

     * Calculate rated tax based on price and tax rate.
     * If you are using price including tax $priceInclude should be true.
     * @param float $price
     * @param float $taxRate
     * @param boolean $priceIncludeTax
     * @param boolean $round
     * @return float
    public function calcTaxAmount($price, $taxRate, $priceIncludeTax = false, $round = true)
        $taxRate = 0.00;

        if (in_array($this->shippingState, $this->taxableStates)) {
            $dots_helper = Mage::helper('DOTS_FastTax/DOTS');
            $taxRate = $dots_helper->getTaxRate();

        if ($priceIncludeTax) {
            $amount = $price * (1 - 1 / (1 + $taxRate));
        } else {
            $amount = $price * $taxRate;

        if ($round) {
            return $this->round($amount);

        return $amount;

In the above implementation, we verify that the shipping state (the state to which the product will ship to) is available in a list of pre-configured taxable states (states to which we would like tax to apply). If so, we use a helper object to get the tax rate. The tax returns a decimal value. Since this is the only method to which we extend from the initial object, I am assuming all other behavior is inherited from the parent.


Is there a way to hide the tax rate on cart summary until the user has engaged the Estimate Shipping and Tax Estimate field?



Go to System > Configuration > Sales > Tax > Default Tax Destination Calculation

Set the following options:

  • Default Country: None
  • Default State: *
  • Default Post Code*

This will hide the default tax amount on initial load. Only until a user requests an estimate does the summary update with the appropriate tax amount.

  • Not working for me on CE Mar 8 '17 at 19:48
  • @SteveRobbins sorry to hear that. Unfortunately I haven't worked with Magento since this post. I do remember this problem existing and it was a pain trying to find an answer. If you do find something that works, be sure to share it :)
    – justinpage
    Mar 8 '17 at 20:51

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