# Time window Learn how to use time-based filters in event expressions. Time windows let you restrict event expressions to events that occurred within a specific time frame. They are useful for checking recent activity or events that happened during a particular period. ## Syntax The syntax for time windows is as follows: | Predicate | Description | | ---------------------------- | -------------------------------------------------------------------------------------- | | `today` | Matches events that occurred today | | `yesterday` | Matches events from yesterday | | `this week` | Matches events in the current calendar week | | `this month` | Matches events in the current calendar month | | `this year` | Matches events in the current calendar year | | `this session` | Matches events in the current SDK session | | `last session` | Matches events from the last closed session | | `last week` | Matches events in the previous calendar week | | `last month` | Matches events in the previous calendar month | | `last year` | Matches events in the previous calendar year | | `in last /**/` | Matches events in a custom [duration](/reference/cql/expressions/durations#time-units) | | `in the last /**/` | Same as above—just an alternative syntax | ## Examples Check if a goal was completed today: ```cql user has completed goal "checkout-started" today ``` Check if a user signed up yesterday: ```cql user has signed up yesterday ``` Check if a product was viewed this session: ```cql user has viewed a product this session ``` Check if a goal was completed last session: ```cql user has completed goal "checkout-started" last session ``` Check if a custom event occurred last week: ```cql user has experienced a custom event "subscription-applied" last week ``` Check if any order was placed in the last 5 days: ```cql user has placed an order in last 5 days ```