---
displayed_sidebar: homepage
---

import TypeList from "@site/src/components/TypeList"

# ITaxCalculationStrategy

## Overview

A tax calculation strategy is used to calculate taxes when calculating a cart's totals. The Medusa
backend provides a tax calculation strategy that handles calculating the taxes, taking into account the
defined tax rates and settings such as whether tax-inclusive pricing is enabled.

You can override the tax calculation strategy to implement different calculation logic or to
integrate a third-party service that handles the tax calculation. You can override it either
in a Medusa backend setup or in a plugin.

A tax calculation strategy should be defined in a TypeScript or JavaScript file created under the `src/strategies` directory.
The class must also implement the `ITaxCalculationStrategy` interface imported from the `@medusajs/medusa` package.

For example, you can create the file `src/strategies/tax-calculation.ts` with the following content:

```ts title="src/strategies/tax-calculation.ts"
import {
  ITaxCalculationStrategy,
  LineItem,
  LineItemTaxLine,
  ShippingMethodTaxLine,
  TaxCalculationContext,
} from "@medusajs/medusa"

class TaxCalculationStrategy
  implements ITaxCalculationStrategy {

  async calculate(
    items: LineItem[],
    taxLines: (ShippingMethodTaxLine | LineItemTaxLine)[],
    calculationContext: TaxCalculationContext
  ): Promise<number> {
    throw new Error("Method not implemented.")
  }

}

export default TaxCalculationStrategy
```

---

## Methods

### calculate

This method calculates the tax amount for a given set of line items under applicable
tax conditions and calculation contexts.

This method is used whenever taxes are calculated. If automatic tax calculation is disabled in a region,
then it's only triggered when taxes are calculated manually as explained in
[this guide](https://docs.medusajs.com/modules/taxes/storefront/manual-calculation).

#### Example

An example of the general implementation of this method in the Medusa backend's tax calculation strategy:

```ts
async calculate(
  items: LineItem[],
  taxLines: (ShippingMethodTaxLine | LineItemTaxLine)[],
  calculationContext: TaxCalculationContext
): Promise<number> {
  const lineItemsTaxLines = taxLines.filter(
    (tl) => "item_id" in tl
  ) as LineItemTaxLine[]
  const shippingMethodsTaxLines = taxLines.filter(
    (tl) => "shipping_method_id" in tl
  ) as ShippingMethodTaxLine[]

  const lineItemsTax = this.calculateLineItemsTax(
    items,
    lineItemsTaxLines,
    calculationContext
  )

  const shippingMethodsTax = this.calculateShippingMethodsTax(
    calculationContext.shipping_methods,
    shippingMethodsTaxLines
  )

  return Math.round(lineItemsTax + shippingMethodsTax)
}
```

#### Parameters

<TypeList types={[{"name":"items","type":"[LineItem](../../entities/classes/entities.LineItem.mdx)[]","description":"The line items to calculate the tax total for.","optional":false,"defaultValue":"","expandable":false,"children":[{"name":"id","type":"`string`","description":"The line item's ID","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"created_at","type":"`Date`","description":"The date with timezone at which the resource was created.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"updated_at","type":"`Date`","description":"The date with timezone at which the resource was updated.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"cart_id","type":"`string`","description":"The ID of the cart that the line item may belongs to.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"cart","type":"[Cart](../../entities/classes/entities.Cart.mdx)","description":"The details of the cart that the line item may belongs to.","optional":false,"defaultValue":"","expandable":true,"children":[]},{"name":"order_id","type":"`null` \\| `string`","description":"The ID of the order that the line item may belongs to.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"order","type":"[Order](../../entities/classes/entities.Order.mdx)","description":"The details of the order that the line item may belongs to.","optional":false,"defaultValue":"","expandable":true,"children":[]},{"name":"swap_id","type":"`string`","description":"The ID of the swap that the line item may belong to.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"swap","type":"[Swap](../../entities/classes/entities.Swap.mdx)","description":"The details of the swap that the line item may belong to.","optional":false,"defaultValue":"","expandable":true,"children":[]},{"name":"claim_order_id","type":"`string`","description":"The ID of the claim that the line item may belong to.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"claim_order","type":"[ClaimOrder](../../entities/classes/entities.ClaimOrder.mdx)","description":"The details of the claim that the line item may belong to.","optional":false,"defaultValue":"","expandable":true,"children":[]},{"name":"tax_lines","type":"[LineItemTaxLine](../../entities/classes/entities.LineItemTaxLine.mdx)[]","description":"The details of the item's tax lines.","optional":false,"defaultValue":"","expandable":true,"children":[]},{"name":"adjustments","type":"[LineItemAdjustment](../../entities/classes/entities.LineItemAdjustment.mdx)[]","description":"The details of the item's adjustments, which are available when a discount is applied on the item.","optional":false,"defaultValue":"","expandable":true,"children":[]},{"name":"title","type":"`string`","description":"The title of the Line Item.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"description","type":"`null` \\| `string`","description":"A more detailed description of the contents of the Line Item.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"thumbnail","type":"`null` \\| `string`","description":"A URL string to a small image of the contents of the Line Item.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"is_return","type":"`boolean`","description":"Is the item being returned","optional":false,"defaultValue":"false","expandable":false,"children":[]},{"name":"is_giftcard","type":"`boolean`","description":"Flag to indicate if the Line Item is a Gift Card.","optional":false,"defaultValue":"false","expandable":false,"children":[]},{"name":"should_merge","type":"`boolean`","description":"Flag to indicate if new Line Items with the same variant should be merged or added as an additional Line Item.","optional":false,"defaultValue":"true","expandable":false,"children":[]},{"name":"allow_discounts","type":"`boolean`","description":"Flag to indicate if the Line Item should be included when doing discount calculations.","optional":false,"defaultValue":"true","expandable":false,"children":[]},{"name":"has_shipping","type":"`null` \\| `boolean`","description":"Flag to indicate if the Line Item has fulfillment associated with it.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"unit_price","type":"`number`","description":"The price of one unit of the content in the Line Item. This should be in the currency defined by the Cart/Order/Swap/Claim that the Line Item belongs to.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"variant_id","type":"`null` \\| `string`","description":"The id of the Product Variant contained in the Line Item.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"variant","type":"[ProductVariant](../../entities/classes/entities.ProductVariant.mdx)","description":"The details of the product variant that this item was created from.","optional":false,"defaultValue":"","expandable":true,"children":[]},{"name":"product_id","type":"`null` \\| `string`","description":"","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"quantity","type":"`number`","description":"The quantity of the content in the Line Item.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"fulfilled_quantity","type":"`null` \\| `number`","description":"The quantity of the Line Item that has been fulfilled.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"returned_quantity","type":"`null` \\| `number`","description":"The quantity of the Line Item that has been returned.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"shipped_quantity","type":"`null` \\| `number`","description":"The quantity of the Line Item that has been shipped.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"metadata","type":"`Record<string, unknown>`","description":"An optional key-value map with additional details","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"includes_tax","type":"`boolean`","description":"Indicates if the line item unit\\_price include tax","optional":false,"defaultValue":"false","expandable":false,"featureFlag":"tax_inclusive_pricing","children":[]},{"name":"original_item_id","type":"`null` \\| `string`","description":"The ID of the original line item. This is useful if the line item belongs to a resource that references an order, such as a return or an order edit.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"order_edit_id","type":"`null` \\| `string`","description":"The ID of the order edit that the item may belong to.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"order_edit","type":"`null` \\| [OrderEdit](../../entities/classes/entities.OrderEdit.mdx)","description":"The details of the order edit.","optional":true,"defaultValue":"","expandable":true,"children":[]},{"name":"refundable","type":"`null` \\| `number`","description":"The amount that can be refunded from the given Line Item. Takes taxes and discounts into consideration.","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"subtotal","type":"`null` \\| `number`","description":"The subtotal of the line item","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"tax_total","type":"`null` \\| `number`","description":"The total of tax of the line item","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"total","type":"`null` \\| `number`","description":"The total amount of the line item","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"original_total","type":"`null` \\| `number`","description":"The original total amount of the line item","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"original_tax_total","type":"`null` \\| `number`","description":"The original tax total amount of the line item","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"discount_total","type":"`null` \\| `number`","description":"The total of discount of the line item rounded","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"raw_discount_total","type":"`null` \\| `number`","description":"The total of discount of the line item","optional":true,"defaultValue":"","expandable":false,"children":[]},{"name":"gift_card_total","type":"`null` \\| `number`","description":"The total of the gift card of the line item","optional":true,"defaultValue":"","expandable":false,"children":[]}]},{"name":"taxLines","type":"([LineItemTaxLine](../../entities/classes/entities.LineItemTaxLine.mdx) \\| [ShippingMethodTaxLine](../../entities/classes/entities.ShippingMethodTaxLine.mdx))[]","description":"The tax lines used for the calculation","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"calculationContext","type":"[TaxCalculationContext](../types/medusa.TaxCalculationContext.mdx)","description":"Other details relevant for the calculation","optional":false,"defaultValue":"","expandable":false,"children":[{"name":"shipping_address","type":"[Address](../../entities/classes/entities.Address.mdx) \\| `null`","description":"The shipping address used in the cart.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"customer","type":"[Customer](../../entities/classes/entities.Customer.mdx)","description":"The customer that the cart belongs to.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"region","type":"[Region](../../entities/classes/entities.Region.mdx)","description":"The cart's region.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"is_return","type":"`boolean`","description":"Whether the cart is used in a return flow.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"shipping_methods","type":"[ShippingMethod](../../entities/classes/entities.ShippingMethod.mdx)[]","description":"The shipping methods used in the cart.","optional":false,"defaultValue":"","expandable":false,"children":[]},{"name":"allocation_map","type":"[LineAllocationsMap](../types/medusa.LineAllocationsMap.mdx)","description":"The gift cards and discounts applied on line items.\nEach object key or property is an ID of a line item","optional":false,"defaultValue":"","expandable":false,"children":[]}]}]} expandUrl="https://docs.medusajs.com/development/entities/repositories#retrieving-a-list-of-records" sectionTitle="calculate"/>

#### Returns

<TypeList types={[{"name":"Promise","type":"Promise&#60;number&#62;","optional":false,"defaultValue":"","description":"The calculated tax total","expandable":false,"children":[{"name":"number","type":"`number`","optional":false,"defaultValue":"","description":"","expandable":false,"children":[]}]}]} expandUrl="https://docs.medusajs.com/development/entities/repositories#retrieving-a-list-of-records" sectionTitle="calculate"/>