Abstract: A method and system for determining customer-facing inventory for online and offline environments are disclosed. Method includes receiving promise engine data and calculating duration of OOS for each hour of day for each product listing ID of product listing identities (IDs), using timestamps received via promise engine data. Method includes analyzing in-stock of products and appending listings to create single in-stock number at product level and dark store level for day. Method includes determining in-stock waterfall at product level and dark store level for day and each hour, and comparing determined in-stock waterfall with inventory data at product level and dark store level for day and each hour/timestamps in day, to isolate symmetrical issues related to visibility of accurate inventory. The method includes outputting decrease in-sale conversion rate and impact of OOS on order loss for products as customer-facing inventory for online/offline environments when the product is in-stock or OOS.