Hi,

Try refer the following code.

class ProductProduct(models.Model):
    _inherit = 'product.product'

    custom_margin = fields.Float(string="Custom Margin")
    list_price = fields.Float(string="Sale Price", compute="_compute_custom_price", store=True)

    @api.depends('standard_price', 'custom_margin')
    def _compute_custom_price(self):
        for product in self:
            product.list_price = product.standard_price * (1 + product.custom_margin)

Regards