Calculate the tax for a transaction before you create the record.

On create and update, DualEntry keeps the tax you send on each line unless you set auto_calculate_tax to required. That setting calculates native US sales tax using DualEntry's tax engine, and Avalara US sales tax, VAT, and GST, then replaces the line tax.

On a record create or update with auto_calculate_tax set to required, a result that is DualEntry's own VAT or GST fails with 422. A calculation that cannot finish also fails with 422.

Use this endpoint to preview the tax, to check the amounts after you choose a VAT or GST rate, or to copy the result onto lines you save yourself.

Required:

• company_id
• customer_id or vendor_id, and not both

Usually also send:

• items, with item_id, quantity, and unit_price on each line
• transaction_buyer_address, transaction_date, and currency_code for US sales tax
• supply_date, to keep the VAT and GST rates that are valid on that date

The response type is SALES_TAX, VAT, GST, or NONE. NONE is still HTTP 200, and the body gives the reason, such as a missing buyer address.

Copy each result line onto items[].tax, and onto expenses[].tax when the record has expenses:

• tax_code to tax.code
• tax_rate to tax.rate
• tax_amount to tax.amount
• is_taxable to tax.is_taxable
• tax_exempt_amount to tax.tax_exempt_amount
• tax_metadata to tax.tax_metadata
• selected_vat_rate_id to tax.vat_rate_id
• selected_gst_tax_rate_id to tax.gst_tax_rate_id

For native Canada GST and VAT, the first response includes available_rates. Choose one and send it on the next call as selected_vat_rate_id or selected_gst_tax_rate_id. On a record line without auto_calculate_tax, send that rate as tax.vat_rate_id or tax.gst_tax_rate_id.

When a write sets auto_calculate_tax to required on a customer transaction, DualEntry reads shipping_address, then billing_address, then the address saved on the customer. If you send neither address, DualEntry copies the customer's saved address to billing_address and shipping_address.

On a vendor record write with auto_calculate_tax set to required, DualEntry reads ship_from_address and ship_to_address, then the addresses saved on the vendor and the company. The write stores only the ship addresses you sent. For a vendor preview on this endpoint, send transaction_ship_from_address and transaction_ship_to_address instead.

For US sales tax on this endpoint, send transaction_buyer_address. DualEntry uses that field and does not fall back to the address saved on the customer.

This endpoint is part of API v2.

{
  "company_id": 1,
  "customer_id": 1,
  "credit_source": {
    "record_id": 1
  },
  "transaction_buyer_address": {
    "postal_code": "94105",
    "city": "San Francisco",
    "line1": "123 Main St",
    "line2": "Suite 100"
  },
  "transaction_ship_from_address": {
    "postal_code": "94105",
    "city": "San Francisco",
    "line1": "123 Main St",
    "line2": "Suite 100"
  },
  "transaction_ship_to_address": {
    "postal_code": "94105",
    "city": "San Francisco",
    "line1": "123 Main St",
    "line2": "Suite 100"
  },
  "transaction_date": "2025-08-29",
  "supply_date": "2025-08-29",
  "items": [
    {
      "discount_type": "PERCENTAGE",
      "discount_value": "10.00",
      "item_id": -1,
      "quantity": "1.000000",
      "unit_price": "100.000000"
    },
    {
      "item_id": -2,
      "quantity": "2.000000",
      "record_level_discount_amount": "5.00",
      "selected_vat_rate_id": 1,
      "unit_price": "50.000000"
    }
  ]
}

{
  "data": {
    "items": [
      {
        "tax_rate": "0.2000",
        "tax_amount": "20",
        "amount_with_tax": "120",
        "tax_exempt_amount": "0"
      }
    ],
    "total_tax_amount": "20",
    "total_with_tax": "120",
    "destination": {
      "postal_code": "94105",
      "city": "San Francisco",
      "line1": "123 Main St",
      "line2": "Suite 100"
    }
  }
}