There are two different ways accounts can be used when you link them to your Acorns app.
The first is your primary checking account. This is the account that we use to fund your investments; you are only able to have one primary checking account linked at a time. We'll use your primary checking account to process your Round-Ups®, One-Time, Recurring Investments, and monthly subscriptions. We recommend linking your personal checking account as your primary checking account. See more information about linking a savings account here. To see what account is linked, go to Settings, then Linked Accounts.
The second way an account can be used is for monitoring Round-Up opportunities. Basically, every time you use a linked checking account, debit card, or credit card, we’ll round up the transaction to the nearest whole dollar. We keep track of that leftover change and, once it adds up to at least $5, we’ll pull that amount of money from your primary checking account and invest it in your Acorns Invest account. You’re able to link up as many checking accounts, debit cards, or credit cards as you like. To review and connect new accounts to monitor for Round-Up opportunities, go to Settings > Linked Accounts.
Please note that if you do not maintain enough funds in your primary checking account to sufficiently cover your Round-Ups® investments, you could incur overdraft fees with your financial institution.