How to calculate import duty (with a worked example)

Duty is not a mystery fee that customs invents at the border. It is a rate, attached to a code, applied to a value. Once you can see those three parts separately, the whole calculation fits on the back of an envelope, and so do the places where it goes wrong. This guide walks the full math on a real shipment.

The three inputs

1. The tariff code. Every duty rate in the world is attached to a code line, not to a product name. Classify the product first; everything downstream inherits from this step. If the code is new to you, start with the plain-English guide to HS codes.
2. The duty rate for your origin. Look up the code in the destination's tariff schedule and read the rate that applies to your origin country: the general (MFN) rate by default, a preferential rate if a trade agreement covers the lane and your goods qualify for origin, or the general rate plus trade-remedy surcharges, such as additional US tariffs on certain Chinese-origin goods.
3. The customs value. Usually the transaction value, what you actually paid for the goods. Some destinations value CIF (goods plus freight plus insurance, common in the EU), others FOB-based (the US uses the goods value). This detail moves real money, so check your destination's convention.

The formula

Duty = customs value × duty rate.
Import VAT or GST = (customs value + duty) × tax rate, where the destination charges one.
Cost of entry = value + duty + tax.

Note the compounding in line two: most VAT regimes tax the duty-inclusive value, so a duty increase raises your VAT bill too.

A worked example

Say you import 1,000 men's knitted cotton t-shirts from Turkey into the United States, at $6 a unit.

• Step 1, classify. Knitted cotton t-shirts sit at 6109.10.00. Knitted keeps them in Chapter 61 (the woven twin would be Chapter 62), cotton keeps them in the .10 subheading (polyester would drop to 6109.90 at roughly double the rate).
• Step 2, the rate. The US general rate for 6109.10.00 is 16.5 percent. Turkey has no US free-trade agreement, so the general rate stands.
• Step 3, the value. 1,000 × $6 = $6,000 customs value.
• Step 4, the duty. $6,000 × 16.5% = $990.
• Step 5, the tax. The US charges no federal import VAT, so the total cost of entry is $6,990. The same shipment into Germany would add 19 percent VAT on the duty-inclusive value: ($6,000 + duty) × 19%.

Now the point of the whole exercise: if that shipment had been misclassified as polyester t-shirts at 32 percent, the duty would be $1,920, an overpayment of $930 on one modest shipment, repeating on every entry until someone rereads the code. Misclassification the other way, underpaying, surfaces later as back duties plus penalties.

Where the calculation goes wrong in practice

• Wrong code. The dominant error, and the quietest. The rate belongs to the code, so every downstream number inherits the mistake.
• Right code, wrong origin treatment. Claiming a preferential rate without meeting the origin rules, or missing a trade-remedy surcharge that applies to your origin.
• Specific and compound rates. Not every line is a simple percentage: some are cents per kilogram, or a percentage plus a specific component. Read the rate column, not just its headline number.
• Valuation misses. Assists, royalties and certain commissions belong in the customs value; getting this wrong understates the duty base.
• Stopping at duty. Duty is one bucket of what the shipment truly costs. Freight, insurance and fees belong in the landed cost formula.

Do it in seconds instead

The import duty calculator runs this entire chain from a plain-English product description: the AI classifies the product, reads the duty rate for your lane, applies the destination's import tax convention, and shows each line of the math separately, with the classification rationale attached. It is an AI best-effort estimate for guidance, not a binding ruling, and it makes the verify-before-filing conversation with your broker a five-minute check instead of a from-scratch lookup.