I hate getting change. Quarters I can stomach, but pennies, nickels, and dimes I find infuriating. I know damn well that they are worth something, and that if I just collected them all and deposited them over time, they would add up to a lot of money. But instead they end up in every corner of the house, under couch cushions and behind the bureau, gathering dust.

A new app being released to the public today, Acorns, can't solve my problem with physical coins, but it does the equivalent with every digital dollar I spend. The app links to any credit or debit card and automatically rounds up purchases to the nearest full dollar, investing the rounded-up cents into a portfolio of index funds. You could always add a lump sum to your account, but the "spare change" approach is meant to gently nudge users toward regular contributions. It's an attempt to take the complex and often expensive process of putting your savings to work and simplifying it down into a mobile app with some basic choices and minimal fees.

Users can swipe through five different options that vary in terms of risk and reward, aiming for a higher return if they have more of a financial cushion to fall back on. But there is no option to pick individual stocks or asset classes. "We don't believe that people can really time the market," says said Jeff Cruttenden, co-founder and COO of Acorns. "We focus less on beating the market and more on index portfolios where we can capture the market and keep fees low."

That's a strategy which is becoming increasingly popular with ordinary investors. Acorns invests in index funds offered by Blackrock and Vanguard, which recently topped $3 trillion in assets, and helped to pioneer the passive approach to retail investing. Unlike going direct with those big names, Acorns has no commissions, no minimum account balances, and no penalties on withdrawals. It charges a flat $1-a-month fee and a 0.25 percent to 0.5 percent management fee on the money invested, compared to the mutual fund average of 1.29 percent.

For most people, being able to afford life's big-ticket items — kids, mortgage, retirement — means putting money into investments that grow in value over time. Realistically most people should start investing in their 20s, but almost half of millennials keep all their money in savings, the equivalent of stuffing cash in your mattress. "In college, I noticed three main reasons why people struggled to start investing," says Cruttenden. "One, people struggled to put together a lump sum to meet minimum account balances; two, commissions make it uneconomical to invest even a few hundred dollars at a time; and three, when people are presented with too many options (thousands of stocks, bonds, etc.) they tend to make no decision or delay it."

The Acorns app hope that a lightweight mobile experience will turn investing into more of a game."You can interact with charts and graphs that communicate risk and return. It's fun." Okay, so it's not exactly Candy Crush, but the real-life rewards are a lot sweeter.