Ad valorem vs specific excise duty

Written by James F. Kollie, Jr. · Published 9 September 2026 · Reviewed 9 September 2026 · 7 min read

The four methods

• Ad valorem. A percentage of a defined base. Rises and falls with value.
• Specific. A fixed amount per unit of quantity — per item, kilogram, ton, litre, gallon, pack or litre of pure alcohol. Indifferent to value.
• Fixed. A flat amount per declaration, consignment or licence, regardless of value or quantity.
• Combined (compound). Two or more of the above applied together, or the higher/lower of two calculations.

Many border charges that are not called "excise" behave in exactly these ways: trade levies, environmental levies, inspection fees, cargo tracking notes and processing fees. Treat them with the same discipline.

Formulas

ad valorem   = base x rate
specific     = quantity x amount per unit
fixed        = amount
combined     = ad valorem + specific
             or max(ad valorem, specific)   ("whichever is higher")
             or min(ad valorem, specific)   ("whichever is lower")

then, where the rule says so:
charge = clamp(charge, minimum, maximum)

The base for an ad valorem excise is defined by the destination and is not always the same as the duty base. It may be the customs value, the customs value plus duty, or a retail-price based value.

Worked examples

Illustrative rates only. Substitute the rules your destination publishes.

1. Ad valorem

Customs value                 30,000.00
Customs duty @ 15%             4,500.00
Excise base = value + duty    34,500.00
Excise @ 10%                   3,450.00

2. Specific, per litre

Quantity                      18,000 litres
Excise                         0.35 per litre
Excise                       6,300.00

Same consignment, value halved to 15,000:
Excise                       6,300.00  (unchanged)

This is the practical point about specific charges: discounting your purchase price does nothing for your excise bill, so a cheap consignment carries a proportionally heavier charge.

3. Fixed with a minimum

Rule: 1.2% of CIF, minimum 190.00
CIF 45,000  ->  540.00        (percentage applies)
CIF 12,000  ->  144.00 -> 190.00  (minimum applies)

4. Combined, "whichever is higher"

Rule: the higher of 25% of value, or 4.00 per kg
Consignment X: value 20,000, weight 3,000 kg
  ad valorem  = 5,000.00
  specific    = 12,000.00
  charge      = 12,000.00   (specific wins)

Consignment Y: value 60,000, weight 800 kg
  ad valorem  = 15,000.00
  specific    =  3,200.00
  charge      = 15,000.00   (ad valorem wins)

Minimums, maximums and rounding

• A minimum turns a small shipment into a disproportionately expensive one. Test your smallest realistic order quantity, not just the full container.
• A maximum caps the charge on large consignments, which can make consolidating shipments genuinely cheaper per unit.
• Apply the clamp after the calculation, and only once. Applying a minimum per line when the rule is per declaration overstates the cost.
• Watch the unit of quantity. Litres versus litres of pure alcohol, gross versus net kilograms, and packs versus sticks are common and expensive mix-ups.

Excise inside the VAT or GST base

In many systems excise sits inside the taxable value for import VAT or GST, so an excise amount is taxed again at the tax rate. The effective cost of a 3,450.00 excise charge under a 15% VAT whose base includes excise is 3,967.50.

excise                     3,450.00
VAT on the excise element    517.50   (3,450 x 15%)
--------------------------------------
effective cost             3,967.50

Whether that applies to you is a destination question. TrueCost lets you switch each excise and levy line into or out of the tax base explicitly, so you can model the rule as written instead of assuming one — see how the import VAT and GST base is built.

Practical checks before you order

1. Get the rule in the destination's own words: method, rate, base, unit and any clamp.
2. Confirm the unit of quantity that will appear on the declaration, and that your packing list expresses quantity in the same unit.
3. Model your smallest and largest realistic order — clamps and methods flip between them.
4. Confirm whether the charge enters the tax base.
5. Record the source and date. Then run the numbers in the free calculator, which supports percentage, per-unit, per-weight, per-volume and fixed rules with minimums and maximums.

How we calculate and verify this

Every figure on this page is produced by the same calculation engine the free calculator and TrueCost Pro use, applied in the sequence set out in our calculation methodology. We publish no duty, excise, levy or tax rates of our own: rates, bases and exemptions are entered by you, and country presets are explanatory starting points that record where they came from and when they were last reviewed.

Results are estimates. This guide explains general method, not the law of any country. Confirm your tariff line, rate, tax base and exemptions with the destination customs authority or a licensed clearing agent before you commit to a purchase or a price. Nothing here is customs, tax or legal advice. If you find something wrong, tell us and we will correct it.