How to Calculate US Import Duty: Formula, Example, Free Calculator
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To calculate US import duty, multiply the customs value of your goods by the duty rate for their HTS code, add any extra tariffs that apply to their origin (such as Section 301 or Section 232), then add the merchandise processing fee (MPF) and, for sea freight, the harbor maintenance fee (HMF). The free US tariff calculator does all four from the official 2026 tariff schedule: pick the HTS code, enter the value and tick the extras.
Below is the formula with a worked example, the value you should actually enter, the 2026 to 2027 fee figures, and the mistakes that make estimates wrong.
The US import duty formula
| Part | How it is worked out |
|---|---|
| Base duty | Ad valorem: customs value × rate. Specific: amount × quantity (for example cents per kg). Compound: both added together |
| Extra duties | Chapter 99 measures in % of value, such as Section 301 or Section 232, when they apply to your goods and country of origin |
| MPF | 0.3464% of value on formal entries, minimum $34.58 and maximum $670.86, for entries from 1 October 2026 |
| HMF | 0.125% of value for goods unloaded at US seaports |
Total cost at the border = base duty + extra duties + MPF + HMF.
Worked example: cotton T-shirts by sea
You import men's cotton T-shirts, HTS 6109.10.00, General rate 16.5%, with a customs value of $10,000, shipped by sea, and a 25% extra duty applies to their origin.
| Line | Calculation | Amount |
|---|---|---|
| Base duty | $10,000 × 16.5% | $1,650.00 |
| Extra duty | $10,000 × 25% | $2,500.00 |
| MPF | $10,000 × 0.3464% = $34.64 (above the $34.58 minimum) | $34.64 |
| HMF | $10,000 × 0.125% | $12.50 |
| Total | $4,197.14 |
That is an effective rate of about 42% on the value of the goods, nearly three times the 16.5% printed in the schedule. This is why calculators that show only the base rate can mislead you badly.
What about per unit and compound rates?
Not every rate is a percent. Some goods pay a fixed amount per kilogram, litre or item, and some pay both:
| Rate type | Example | Duty on 500 kg worth $10,000 |
|---|---|---|
| Ad valorem | 16.5% | $1,650 |
| Specific | 2.2¢/kg | 500 × $0.022 = $11 |
| Compound | 2.2¢/kg + 5% | $11 + $500 = $511 |
For specific and compound rates you need the quantity in the unit the schedule uses, so take the net weight or count from your packing list rather than the gross shipping weight, unless the schedule says otherwise for that line.
How to use the tariff calculator
- Open the tariff calculator.
- Pick the HTS code. Not sure of it? Search the HTS code lookup first, or start from a plain description with the AI HS code finder.
- Choose the rate column: General for most countries, Special if your goods qualify under a trade program, Column 2 for countries without normal trade relations.
- Enter the customs value and, for per unit rates, the quantity.
- Tick the chapter 99 extra duties that apply to your goods and origin, or add your own percent.
- Keep MPF ticked for a formal entry and HMF ticked for sea freight.
- Read the total, then copy it or save it as a PDF.
The calculator handles percent, per unit and compound rates. About 2 in 100 HTS rates are written in a way no calculator can apply on its own, for example a rate charged "on the case" of a watch. The calculator tells you, and you choose "My own rate" to enter the figure.
Which value do you enter?
US duty is charged on the transaction value: the price actually paid for the goods. International freight and insurance are generally not included when they are shown separately. In practice that is close to the FOB value.
| You bought on | What to enter |
|---|---|
| FOB | The invoice value |
| CIF | The invoice value minus freight and insurance |
| EXW | The invoice value; ask your broker how any costs before the port should be treated |
Assists, royalties and selling commissions paid by the buyer can add to the value. Many other countries, such as EU members, charge duty on the CIF value instead, so do not reuse this rule abroad.
Formal or informal entry: does the MPF apply?
Shipments valued over $2,500, and some goods at any value, need a formal entry. Those pay the MPF at 0.3464% with the minimum and maximum above. Smaller shipments may go through an informal entry with a lower flat fee; untick MPF in that case. The HMF applies only to cargo unloaded at US seaports, not to air or truck shipments.
The MPF figures change every 1 October with the US government fiscal year, so check the date on any number you find online.
Why your estimate might differ from the broker's bill
- Extra duties by origin. Many chapter 99 measures apply by country of origin even when the code has no footnote. Confirm the current position before you ship, because these measures change often.
- Wrong HTS code. A different heading can mean a different rate.
- Value adjustments. Assists or royalties added by CBP raise the duty.
- Broker fees. The customs broker charges for filing the entry. That is a service fee, not duty.
- Freight, insurance and delivery. These are part of your landed cost but not part of the duty.
For a full cost per unit, add freight, insurance and broker fees on top of the calculator's total. Our page on landed cost shows how.
Calculate your import duty now
Pick the code, enter the value, tick the extras and you will see the real border cost of a shipment in a minute. Try the free US tariff calculator, then put the final figures on your commercial invoice and quote with confidence. Your customs broker files the entry and confirms the final amount.
Frequently asked questions
How is US import duty calculated?
Multiply the customs value by the HTS duty rate (or the per unit rate by the quantity), add any chapter 99 extra duties for the origin, then add the merchandise processing fee and, for sea freight, the harbor maintenance fee.
What is the MPF for 2026 to 2027?
For formal entries from 1 October 2026 the merchandise processing fee is 0.3464% of value, with a minimum of $34.58 and a maximum of $670.86 per entry.
Is US duty charged on freight?
Generally not. US duty is charged on the price paid for the goods, without international freight and insurance when they are shown separately. Many other countries charge duty on the CIF value.
Does the HMF apply to air freight?
No. The harbor maintenance fee of 0.125% applies only to goods unloaded at US seaports, not to air or land shipments.
Why is my broker's bill higher than my estimate?
Common reasons are extra duties that apply by country of origin, a different HTS code, value adjustments such as assists, and the broker's own filing fee, which is a service charge rather than duty.