How can I map the birthdate field?

The birthday field type in Mailchimp is specifically designed to hold only the date and month of a person's birthdate, excluding the year. This limitation is important to remember, especially if you're planning to integrate Mailchimp data with Salesforce. 

To store a full birthdate, Mailchimp recommends creating a new custom merge field with the date data type. Mailchimp date fields require a year, which matches the standard date formats used in Salesforce. 

Mailchimp to Salesforce mapping:

Depending on the format of the data you need in Mailchimp, you have two options:

• Full date: Create a new date merge field in Mailchimp to store the full birthdate format, including year. That Mailchimp date can be mapped to a Salesforce date field, and we will handle the locale formatting.
• Month and Day only: Map a Mailchimp birthday merge field to a Salesforce text field to accommodate the missing year.

Salesforce to Mailchimp mapping: (data wizard or SF>MC field mappings)

• If you map a Salesforce date field to a Mailchimp birthday field, we will remove the year and only map day and month. 
• If you need to keep the year when syncing, use a date field on both sides.
• You can't map Salesforce text fields to Mailchimp birthday fields, even if your field data conforms to the birthday field format (MM/DD or DD/MM).

Note: The integration can make new Mailchimp merge fields for you, without leaving Salesforce.