How we actually calculate your tariff.
Every tariff calculator hides something. This page is the opposite — we walk through the formula, the sources, the update cadence, the limitations, and the specific scenarios where you should not trust the number we give you.
Why a tariff calculator should show its work
US import duty isn’t one number — it’s up to four numbers stacked together, plus a constantly shifting overlay of executive orders, AD/CVD orders, and USTR exclusions. Most "duty calculators" quote a single MFN rate and call it a day. Sellers importing from China then get blindsided at the port when the real landed cost is several times what the calculator said.
We think that's unacceptable. A decision tool has to show how it reached the answer, what's changing, and where it could be wrong. Otherwise it's just a magic 8-ball with a database behind it.
"A decision tool is either transparent or it’s a marketing site. We’d rather you argue with our numbers than trust them blindly."
Four duties, summed on customs value
For any single import, the effective ad-valorem duty is the sum of four independent components, each applied to the declared customs value:
Each term can be 0 for a given import. A cotton t-shirt from Vietnam pays only MFN. A Bluetooth speaker from China pays MFN + §301 + IEEPA. Some preference programs (USMCA, GSP, KORUS) zero out MFN — but do not affect §301 or IEEPA. This is the single most common source of seller surprise.
$10,000 of Bluetooth speakers from China
Product: portable Bluetooth speakers. HTS: 8518.22.0000. Declared value: $10,000. Origin: China.
MFN base rate is duty-free under the Information Technology Agreement, so the column rate adds $0. Section 301 List 4A (HTSUS 9903.88.03) adds +7.5% = $750. IEEPA China declaration (HTSUS 9903.01.25) adds +20.0% = $2,000. AD/CVD has no active order on this HTS from China — Duty surfaces this but doesn’t auto-compute case-by-case rates.
Total ad-valorem duty: $2,750. Effective rate: 27.5%. The same shipment from Vietnam pays $0 in column duty and is the most common arbitrage move sellers consider.
Every number traces back to a .gov document
We do not invent rates. Every number you see clicks through to a primary source — either a USITC HTS line or a Federal Register notice. Here is what we currently sync into Duty:
We do not use third-party data brokers or scraped consolidator databases. Every calculation can be verified against a primary government document.
How quickly new tariffs reach your calculation
UPDATED WITHIN 6 HOURS
- Federal Register tariff notices
- IEEPA executive orders
- USTR §301 rate changes & exclusions
- Presidential proclamations (§232, §201, reciprocal)
UPDATED WEEKLY OR ON DEMAND
- USITC HTS revisions (quarterly / as-issued)
- Special program eligibility (USMCA / KORUS / GSP)
- Chapter origin-share refreshes from Census trade data
- AD/CVD orders — surfaced but not auto-computed
When a rate changes, we mark it on the change docket and flag affected HTS codes for 30 days. Saved-SKU subscribers get email alerts within 6 hours of publication.
Where Duty’s number is wrong, by design
We are precise about what we can and cannot tell you:
WE CAN TELL YOU
- The current MFN rate for a specific HTS code
- Whether §301 applies and at what rate
- Whether IEEPA currently applies to this origin
- Whether an FTA could zero out MFN
- Recent Federal Register notices touching the HTS
WE CANNOT TELL YOU
- Whether your product will be classified as HTS X by a CBP officer at port
- Whether your origin claim will withstand a CBP audit
- Your AD/CVD rate if your specific producer isn’t named in the order
- Whether a pending scope ruling will include your product
- Any state-level tax, excise, or FDA / FCC compliance cost
This site is a decision tool, not a licensed broker.
The numbers we show are accurate against the rules as-published. They are not a substitute for a binding ruling from CBP or advice from a licensed customs broker, and we do not assume liability for entry decisions based on our calculations.
For shipments above $10,000 or in active AD/CVD-covered categories, get a binding CBP ruling before the first entry.
When we are wrong, here is what happens
Tariff rules are messy. We expect to be wrong occasionally. If you can cite a specific HTS code, a Federal Register notice, or a CBP ruling that contradicts our output, we will:
- Acknowledge within 24 hours.
- Investigate against the cited source.
- If confirmed, push a fix and log it in the change docket within 48 hours.
- Re-issue the affected SSR pages so search and AI crawlers see the correction immediately.
The short answer: don’t. Verify.
"Trust us" is not a methodology. Here's what we offer instead:
Every rate links to a primary source. Click any duty line in the calculator and you will land on a USITC, USTR, or Federal Register document. If a rate doesn't link anywhere, that's a bug — report it.
Our changelog is public. Every rate change, every methodology update, every correction is in the change docket.
We publish uncertainty. When an HTS line is missing data, when special-rate eligibility hasn't been qualified, or when a Chapter 99 rule has an effective date, we flag it in the calculation. You won't be surprised.
"Go read our sources. Click the links. Disagree with our math. That is the only review process that matters."