What Discount property means in Google Analytics 4?

Question

GA 4 has few events that have discount property. From the official documentation: https://developers.google.com/gtagjs/reference/ga4-events#purchase

Discount - Monetary value of discount associated with a purchase.

But how it works with Price / Value properties?

I want to log that I sold a product costing 1000 EUR with 10% discount. Should I report Discount 100, Price & Value 1000? Or maybe Price/Value should be 1100 and then Discount 100?

Answer 1

TL;DR

Purchasing a $1,000 product with a 10% discount should be tracked as a $900 price & $100 discount:

{
    value: 900,
    items: [{
        price: 900,
        discount: 100,
        quantity: 1
    }]
}

and purchasing two would be tracked as:

{
    value: 1800,
    items: [{
        price: 900,
        discount: 100,
        quantity: 2
    }]
}

Explanation

It looks like the GA4 documentation & examples provide some contradictory information.

GA4 > Recommended Events > purchase example shows that the ecommerce.value would be calculated as the sum of the ecommerce.items[] (price - discount) * quantity

However, their Apply a discount to an ecommerce event article shows that the ecommerce.value would be calculated as the sum of the ecommerce.items[] price * quantity.

Google Analytics use the ecommerce.item's price & quantity to determine "Item Revenue" metric on Ecommerce Reports. The Ecommerce purchases report, calculates the "Item revenue" metric as:

Item revenue = price x quantity

• Price is the price parameter for an item in the items array
• Quantity is the quantity parameter for an item in the items array

Ultimately, it depends on how you would like to define & calculate "Item Revenue" within in your Google Analytics Reports, but with revenue meaning, "the total amount of money a business earns from the sale of goods or services", and not the total retail/MSRP value of the items purchased, then it would make sense then to use the example provided by Apply a discount to an ecommerce event that shows that the "Item Revenue" & ecommerce.value would be calculated as the sum of the ecommerce.items[] price * quantity and NOT (price - discount) * quantity.