# Acceptable date and timestamp formats for profile and event properties Learn acceptable date and timestamp formats for profile properties added via API. ## Acceptable date and timestamp formats When adding an event or profile property to Klaviyo via API, you must use one of the recognized formats outlined below with a few notable exceptions. Event datetime sent via the [Create Client Event API](https://developers.klaviyo.com/en/reference/create_client_event) and the [Create Event API](https://developers.klaviyo.com/en/reference/create_event) must be in ISO 8601 format: `YYYY-MM-DDTHH:MM:SS.mmmmmm`. Note that event datetimes sent via the legacy v1/v2 endpoints support a Unix timestamp in addition to datetime ISO 8601 format, while our newest set of APIs do not support Unix timestamps. When using JSON:API filtering in your requests, input a `datetime` or a `timestamp`, depending on the filter. `Datetime` is formatted in ISO 8601 format, such as `YYYY-MM-DDTHH:MM:SS.[mmm]`. Some examples include: * `2018-12-27` * `2018-12-27T12:30:00` * `2018-12-27T12:30:00Z` * `2018-12-27T12:30:00.710` * `2018-12-27T12:30:00.710Z` * `2018-12-27T12:30:00+03:00` `Timestamp` is formatted as a Unix Epoch time such as `978354000`. ### Missing or improperly formatted date and timestamp data If the hour, minute, or second, is not included in the event's datetime values, any empty data will default to `0`. For example, a timestamp of `2021-09-15T13:34` will be ingested as `2021-09-15T13:34:00`. A timestamp of `2021-09-15` will be ingested as `2021-09-15T00:00:00`. When you import a date without a timestamp, a default time of midnight UTC is applied to the date when it is mapped to the `date` data type. This may cause date-property triggered flows to send a day early or late depending on the account’s timezone. When you have a date with no associated timestamp to ingest, we recommend amending a timestamp of `12:00:00` for the best outcome in a date-property triggered flow. ### Considerations for CSV files If you need help reformatting your dates in a spreadsheet before uploading your CSV file, head to our article, Format dates for CSV files. For more information on uploading a CSV file to Klaviyo, head to our article on how to add subscribers to an existing list. ## Additional resources * Format dates for CSV files * How to run a multinational business