Starting in January 2026, you can now use Chimpegration to add/update date-based merge fields in Mailchimp and have those date-based merge fields be added/updated to a relevant field in Raiser's Edge
As long as the Date-based Merge Field is in the same format that your Raiser's Edge uses (dd/MM/yyyy or MM/dd/yyyy), then you can use a Mailchimp Data Update process or a Raiser's Edge Data Update process to add/update a date on Raiser's Edge or Mailchimp. To do this, run either of the process mentioned and when you get the Field Mapping step, be sure to map a Date-based Merge Field in Mailchimp to the appropriate Date-based field in Raiser's Edge.
When running a Mailchimp Data Update process, please consider which NXT source you are going to use. Some dates are included as part of standard fields included in Constituent Lists, but the are limited. You will more likely going to need to use a Query to get the right output/field select you need. With this in mind, you will need to have included any relevant date fields as an output fields with the Query you are using.