Hot investing app Acorns just snagged Airbnb to give its customers 'free money'

Popular micro-investing app Acorns has snagged Airbnb for its rewards program.

The program, called "Found Money," gets Acorns users bonus investment cash when they use services like Blue Apron, Hotel Tonight, Jet.com, 1-800-Flowers, and soon Hulu.

For Airbnb, the partnership works in two ways:

• Airbnb hosts will get $50 invested in their Acorns account when they host their first booking.
• Airbnb guests get 15% of the Guest Service Fee put into their Acorns account (if they book the stay through the Acorns app).

In April, Acorns saw a big investment from industry giant PayPal, which contributed the majority of a $30 million round that brought Acorns' total funding to $62 million. Acorns' basic strategy is using ETFs and an attractive mobile interface to narrow the investing decision for users down to two questions: "how much" they want to invest, and "how much risk" they want to take.

'Free Money'

"Found Money" works much like a credit card reward system, but instead of cash back, users get money put directly into their Acorns investment account.

The program launched a beta in May, and Acorns' chief commercial officer Manning Field says all its five beta partners signed onto the full program.

CEO Noah Kerner previously said the new initiative fits into Acorns' broader goal of allowing investments to automatically happen in the background of its customers' lives. One of Acorns' core strategies has been building up account balances using "round-ups." Acorns can monitor purchases on its users' credit and debit cards and invest the difference - if someone spends $8.46 on lunch, Acorns can invest the $0.54.

The brands are footing 100% of the bill for these rewards. So what's in it for them? Field says the partnership has seen a greater than 50% average lift in transactions for Acorns customers.

Acorns has opened 1.2 million investment accounts, about 75% of which belong to millennials. The service costs $1 a month for accounts less than $5,000, or 0.25% of account assets a year on those over that. But if you are a student, or are 18 to 23 years old, it is free.