Editorial Policy & Data Sources

Data Sources and Methodology

CalcMyTariff.com draws from three primary authoritative sources. No rate is published unless confirmed across at least two of these sources:

(a) Tax Foundation Tariff Tracker (taxfoundation.org) — Country-level effective tariff rates derived from all active executive orders, trade proclamations, and legislative changes. The Tax Foundation updates their tracker in near-real time when new trade actions are announced.
(b) USITC Harmonized Tariff Schedule (usitc.gov) — The official HTSUS published by the United States International Trade Commission is the authoritative source for MFN (Most Favored Nation) base rates and product-level HTS code classifications. All MFN rates in our database are derived from HTSUS chapter rates.
(c) Penn Wharton Budget Model (University of Pennsylvania) — Trade volume modeling and economic impact analysis. Used for context and cross-verification of effective rate estimates, particularly for bilateral trade deal impacts and Section 301 coverage modeling.

Calculation Verification

The tariff stacking engine is tested against 38 known customs scenarios with exact expected outputs. Any engine change must pass all verification cases before deployment. Test scenarios include:

→Steel from China (78%): MFN 3% + S232 50% + S301 25% = 78%
→Electronics from China: MFN rate + S122 15% + S301 additional rates
→USMCA auto parts from Mexico: 0% (USMCA short-circuit, all other rates bypassed)
→Wine from France: MFN 4.5% + S122 15% surcharge
→Furniture from Vietnam: MFN rate + S122 15% (no S232, no S301)

Engine test results are run before every deployment. All 38 scenarios must pass with exact expected values — not approximations.

Update Frequency

Tariff rates are reviewed whenever new executive orders, trade proclamations, or legislative changes are announced — these can happen with no advance notice.

Pages automatically refresh via ISR (Incremental Static Regeneration) within one hour of a data update. This means if we update our data files, all 15,000+ pages will reflect the new rates within 60 minutes — without a full site rebuild.

The “Last verified” date shown at the bottom of each page reflects when rates were manually confirmed against official sources — NOT an automated build timestamp. This date changes only when a human has actually re-verified the rates against Tax Foundation, USITC, or CBP.

Tariff Stacking Formula

Total Tariff = MFN Base Rate + max(S122 Surcharge, S232 Duties, Bilateral Deal Rate) + S301 Additional Tariffs (China only)

MFN (Most Favored Nation): Base WTO-bound tariff rate applicable to all countries that haven't negotiated a preferential deal.
Section 122 Global Surcharge: Uniform surcharge enacted February 24, 2026 under the Trade Act. Applies globally except where superseded by a higher bilateral deal rate. Section 232 products are excluded from Section 122. Expires approximately July 24, 2026 (150 days from enactment).
Section 232 Duties: Product-specific national security duties: steel (50%), aluminum (50%), copper, lumber, and autos. Section 232 products are excluded from the Section 122 surcharge — they cannot stack.
Bilateral Deal Rate: Country-specific negotiated rates. If a bilateral deal imposes a higher rate than Section 122, the bilateral rate applies and Section 122 is waived.
Section 301: Additional tariffs on Chinese goods only. Stacks on top of MFN + whichever of (S122, S232, bilateral) applies. Section 301 does not apply to non-China origins.
USMCA: Qualifying goods from Canada or Mexico receive 0% under USMCA — all other tariff stacking is bypassed for USMCA-eligible goods.

HTS Code Classification Limitations

CalcMyTariff.com uses 75 broad product categories designed to cover the most common US import types. These categories map to HTS chapters (2-digit codes) and sections, not to precise 10-digit HTS subheadings.

The Harmonized Tariff Schedule of the United States (HTSUS) contains over 17,000 distinct product classifications. A single product category on CalcMyTariff.com (e.g., “electronics”) may cover hundreds of individual 10-digit HTS subheadings with meaningfully different duty rates.

For precise duty classification: importers should consult the full USITC Harmonized Tariff Schedule at htsus.usitc.gov or work with a licensed customs broker. Our 500 HTS code lookup tool covers the most commonly searched codes but is not exhaustive.

CalcMyTariff.com rates are for planning and estimation purposes. For binding tariff classifications and official duty determinations, consult U.S. Customs and Border Protection (CBP) or a licensed customs broker.

Corrections Policy

Errors are corrected immediately upon discovery. All corrections are verified against official government sources before the updated rate is published — we do not accept unverified user reports as grounds for rate changes.

If you believe a tariff rate is incorrect, please contact us with: the specific page URL, the rate you believe is wrong, and the official source showing the correct rate. Corrections are documented in our update feed at /updates.