Tax Fixed Amount Multiplier

This module adds a multiplier option to fixed-amount taxes, controlling how the line quantity is used in the tax computation.

By default, Odoo computes fixed taxes as line quantity × amount. This module allows choosing between four multiplier modes:

No Multiplier: the amount is applied once per line, regardless of quantity. Useful for per-document fees (e.g., stamp duties).
Quantity (default): standard behavior, equivalent to line quantity × amount.
Product Quantity: the line quantity is first converted to the product's unit of measure before multiplying. This is useful when the tax is defined per unit of the product, but the line may use a different UoM (e.g., selling in dozens while the product is defined in units).
Product Weight: multiplied by the total weight of the products on the line (product quantity × product weight). Useful for weight-based fees such as environmental levies.

This module is compatible with account_tax_fixed_amount_currency without depending on it. When both modules are installed, the selected multiplier changes the fixed-tax quantity first, and the currency module can then convert the resulting fixed amount to the document currency through the normal tax computation chain.

[!IMPORTANT] This is an alpha version, the data model and design can change at any time without warning. Only for development or testing purpose, do not use in production. More details on development status

Table of contents

Use Cases / Context

In standard Odoo, fixed-amount taxes are multiplied by the line quantity as entered on the document. This means that if a product is sold in dozens, the tax is multiplied by 1 (the line quantity) instead of 12 (the actual number of units).

This can be problematic for taxes or fees that are defined per unit of product, such as:

Per-unit recycling fees: a fixed fee per unit sold, regardless of the unit of measure used on the sales line.
Per-kilogram levies: a fee based on the total weight of the products sold (e.g., environmental taxes on volatile organic compounds).
Per-document stamps or duties: a fixed fee applied once per line, regardless of the quantity.

This module addresses these use cases by allowing to control how the quantity is interpreted in the tax computation.

Configuration

To configure this module, you need to:

Go to Invoicing > Configuration > Taxes.
Open or create a tax with Tax Computation set to Fixed.
Set the Amount Multiplier field to the desired mode:
- No Multiplier: the tax amount is applied once per line.
- Quantity (default): standard behavior, multiplied by the line quantity regardless of the unit of measure.
- Product Quantity: the line quantity is converted to the product's unit of measure before multiplying.
- Product Weight: multiplied by the total weight (product quantity × product weight).

Usage

Product Quantity mode is useful for per-unit taxes where the product may be sold in different units of measure.

For example, if a product is defined in Units and has a per-unit tax of 5.00, selling 1 Dozen will compute the tax as:

1 dozen = 12 units → tax = 12 × 5.00 = 60.00

This also works with nested UoM hierarchies. For example, selling 1 Box of 10 Dozens will compute:

1 box = 10 dozens = 120 units → tax = 120 × 5.00 = 600.00

Product Weight mode is useful for weight-based fees. For example, with a levy of 3.00 per kilogram and a product weighing 2.5 kg:

10 units × 2.5 kg/unit × 3.00/kg = 75.00

If account_tax_fixed_amount_currency is also installed, configure the fixed tax currency on the tax as usual. The multiplier changes the quantity used by the fixed tax computation, and the resulting amount is then converted by the currency module.

Bug Tracker

Bugs are tracked on GitHub Issues. In case of trouble, please check there if your issue has already been reported. If you spotted it first, help us to smash it by providing a detailed and welcomed feedback.

Do not contact contributors directly about support or help with technical issues.

Credits

Authors

Camptocamp

Contributors

Iván Todorovich <<ivan.todorovich@camptocamp.com>>

Maintainers

This module is maintained by the OCA.

OCA, or the Odoo Community Association, is a nonprofit organization whose mission is to support the collaborative development of Odoo features and promote its widespread use.

Current maintainer:

This module is part of the OCA/account-invoicing project on GitHub.

You are welcome to contribute. To learn how please visit <https://odoo-community.org/page/Contribute>.