Hi,

You can achieve this with a lightweight Odoo customization using @api.onchange.

Here’s the Python code for a small module that adds this behavior.

from odoo import api, fields, models

class SaleOrderLine(models.Model):

    _inherit = "sale.order.line"

    final_price = fields.Float(

        string="Final Unit Price",

        help="Enter the final selling price per unit; discount will be calculated automatically."

    )

    @api.onchange('final_price')

    def _onchange_final_price(self):

        for line in self:

            if line.final_price and line.product_id:

                list_price = line.product_id.lst_price

                if list_price > 0:

                    discount = (1 - (line.final_price / list_price)) * 100

                    line.discount = discount

                    line.price_unit = list_price

                else:

                    line.discount = 0.0

* Adds a new field final_price on sale order lines.

* When you enter a final_price, it:

          -Sets the Unit Price to the product’s list price.

          -Calculates and fills the Discount % field automatically.

* This ensures accounting, taxes, and reports continue to use Odoo’s built-in fields.

Option 2 — Odoo Studio (No Code Alternative)

If you use Odoo Enterprise, you can implement a simpler version with Odoo Studio:

    Open Sales → Orders → Order Lines.

    Activate Studio and add a new field called Final Price.

    Add an Automated Action (triggered on change of Final Price) with Python code:

if record.product_id and record.final_price:

    list_price = record.product_id.list_price or 0

    if list_price > 0:

        record.discount = (1 - (record.final_price / list_price)) * 100

        record.price_unit = list_price

    Save and test — when you edit Final Price, Odoo will auto-calculate the discount.

Related module:-

* https://apps.odoo.com/apps/modules/18.0/sale_discount_total

Hope it heps