Overview

Amazon’s Selling Partner API now includes a unitOnTimeDeliveryRate field in the Seller Performance Report. The metric moves delivery tracking from the order level to each individual unit, giving sellers a more precise view of fulfillment reliability. The change is live for the United States marketplace, and it matters because on‑time delivery remains a key component of Amazon’s account health score.

Key Points

• Unit‑level on‑time rate added — The GET_V2_SELLER_PERFORMANCE_REPORT endpoint now returns a percentage called unitOnTimeDeliveryRate that reflects each shipped unit’s timeliness.
• More realistic performance picture — In a five‑item order where four items arrive on schedule and one is late, the new metric records an 80 % on‑time rate instead of flagging the whole order as a miss.
• US‑only rollout — The field appears only in responses for the United States marketplace; no public timeline exists for Europe, Japan, or other regions.
• Backward compatible — Existing report responses keep all previous fields; developers only need to add parsing logic for the new attribute.
• Impact on multi‑item sellers — Merchants that frequently ship bundles or mixed‑SKU orders gain a clearer signal of which specific items are causing delays.
• Enables targeted operational fixes — The granularity helps identify problematic warehouses, carriers, or product categories without over‑hauling the entire fulfillment network.

How Unit‑On‑Time Delivery Rate Works

1. Report request — When a seller calls GET_V2_SELLER_PERFORMANCE_REPORT for the US marketplace, the JSON payload now contains a unitOnTimeDeliveryRate key alongside the traditional orderOnTimeDeliveryRate.
2. Percentage calculation — Amazon divides the total number of units delivered on or before the promised delivery date by the total units shipped in the reporting period, then multiplies by 100. For example, if 12,340 out of 13,500 units arrived on time, the field returns .