The Last 28 Days filter is located in the Date Filter
The Last 28 Days option shows culminated data results from the past 28 days.
We aim to release daily data within 72 hours after the end of a specific date (EST time zone). For example, data for the 14th of a month would be published by the end of the day on the 17th (EST).
The Last 28 Days filter is available on the paid version of SimilarWeb and on the SimilarWeb API.
Last 28 Days setting from the UI: