how exactly does borrowing of properties work again?

Hi Tobias, Please stand by as I search the Mixpanel knowledge base for an AI-powered answer. I normally take about 15 seconds or so. In case AI cannot answer your question, feel free to reach out to Mixpanel support at mixpanel.com/get-support. If you have follow-up questions for this thread, please tag me again with your question: @kapa.ai <follow-up question> 👋

Borrowed Properties allow you to "borrow" a property from a prior event and automatically associate it with a future event at query time. This eliminates the need to explicitly track the same property on every single event, which is particularly useful for merging client-side context with server-side or warehouse events [Borrowed Properties Intro; Custom Properties].

** Most Recent Value: A borrowed property captures the value from the most recent occurrence of the source event. For example, if you borrow "Search Term" from a "Product Searched" event to use on a "Purchase" event, Mixpanel looks for the last time that user performed a search [Custom Properties]. ** 7-Day Lookback Window: There is a fixed 7-day lookback window. If the source event (e.g., the search) occurred more than seven days before the destination event (e.g., the purchase), the property will return as (not set) [Custom Properties]. ** *Retroactive and On-the-Fly: These properties are calculated at query time. This means they work fully retroactively on your existing data and do not require any code changes from your engineering team [Evolving Data Model].

** Roles: Only users with Owner or Admin roles can create or drop borrowed properties [Project Roles; Custom Properties]. ** Limits: Each Mixpanel project is limited to a maximum of 20 borrowed properties [Custom Properties]. ** Availability: This feature is available for customers on *Growth and Enterprise plans [Getting Started].

** Bridging Data Sources: Attributing client-side properties (like UTM tags or device info) to server-side events that lack that context [Warehouse Connectors]. ** Experimentation: Mixpanel’s Experiment reports use borrowed properties under the hood to attribute user behavior to specific variants after an $experiment_started event is triggered [Experiments Deep-Dive]. ** *State Tracking: Tracking a state (like "Dark Mode: Enabled") once and applying it to all subsequent actions without re-sending that property every time [Custom Properties].

ℹ️ Tip: Mention @kapa.ai in the thread for follow-ups or DM the app for 1-to-1 help.