Accumulation / Cumulation

Accumulation (also called cumulation) is a preferential origin principle that allows materials originating in one FTA party to be treated as originating when used in production by another party. It enables regional supply chains by treating inputs from any party as "home-country" inputs for tariff shift and regional value content calculations.

The most common form is bilateral or regional accumulation — used in USMCA, KORUS, and CAFTA-DR. Under USMCA Article 4.6, materials originating in Canada, Mexico, or the United States are treated as originating when used in another USMCA party's production.

Variations include:

• Bilateral accumulation — two parties only (most U.S. bilateral FTAs)
• Diagonal accumulation — extended to multiple FTAs sharing harmonized origin rules (rare in U.S. agreements; common in EU framework)
• Full accumulation — also allows the processing operations (not just materials) performed in another party to count toward originating status

CAFTA-DR and USMCA both allow accumulation of materials. CAFTA-DR additionally permits limited accumulation with Mexico (for certain textile and apparel products).

To use accumulation:

1. The materials must qualify as originating under the FTA's rules (in the originating party)
2. The producer must obtain supporting documentation from the supplier (e.g., a supplier's declaration or certification)
3. The materials are then treated as originating throughout the rest of the production process

Without accumulation, regional supply chains would be penalized — for example, a Mexican producer using Canadian-origin steel would have to count that steel as "non-originating" even though it qualifies under USMCA.

CBP verifications often focus on supplier documentation supporting accumulation claims. Loss of accumulation eligibility can cascade — a single misclassified input can disqualify a downstream good's preferential treatment.