The account holder that opened the joint account is designated as the primary account holder. To see who the primary account holder is, log in and navigate to Settings > Accounts.
We aren’t able to transfer primary ownership of a joint account once it’s been created. However, remember that a joint account is legally owned by both parties associated with the account. The IRS requires only the primary account holder be listed on tax statements. (Publication 550, page 3)
Both account holders will receive the 1099-B, 1099-DIV, and/or 1099-INT tax documents associated with the joint account in their Betterment Documents section. Integrations with tax preparation software will pull these documents from both accounts, so you will want to be sure to avoid duplicate tax forms if you import your tax documents at tax time. (See “Importing Joint Accounts”)
We cannot change the primary account holder on a joint account. Since Betterment is not a tax advisor, we highly recommend consulting with a tax professional for further questions regarding how to file your taxes in a joint account.