About 70% of Americans live paycheck to paycheck, and about 70% of Americans can’t afford an unexpected $500 expense, according to a recent Bankrate survey.

Those are scary statistics. And while I’m not in those two categories, I’m not far beyond them—that is, I’m a single millennial living in expensive New York City, and I don’t have much of a cushion in my bank account, and while a $500 expense would not wipe me out, it would do serious damage. In other words, I need to start saving more money, as do most Americans.

Here at Yahoo Finance, July has been our “Ways to Save” month. All month, we’ve run stories and videos on saving strategies, and we’ve asked our readers how they save.

For my own efforts, I’ve been using three very different mobile apps, each of which can help you set aside some money. I’ve had varied results.

Acorns for investing in equities



Acorns has raised nearly $62 million in funding since it launched in 2012, and it is by far the best known of the three apps I used.

View photos Payoff_digit More

The app works by rounding up your spare change (that is, the difference between a transaction total and the next whole dollar amount) and investing it in a portfolio of funds and equities, commission-free. So: If you’ve set your roundup limit at 30 cents, then when you pay $22.70 at the grocery store, Acorns puts 30 cents into the investment portfolio. You don’t even feel it.

But allowing automatic roundups still makes me a little nervous (what if I use my credit card a lot in one month, and suddenly I see a high total has gone in to Acorns?) so I’ve limited Acorns thus far. After a couple months of using it, I have just over $30 in my account.

Acorns is credited with making the “roundup” app a popular model that other companies have followed.

Lawnmower for investing in digital currency

Lawnmower began as a roundup app, like Acorns—but for investing in bitcoin. The app, through a plug-in with leading bitcoin wallet Coinbase, would use your spare change to invest in bitcoin.

View photos Lawnmower More

I’ve covered digital currency extensively, so I know more about it than the average layperson knows or cares to know. It’s certainly not for everyone. I’m not sure I’d recommend buying bitcoin to my parents. And yet: bitcoin is up 120% in the last year. It might just be a good speculative investment, even if you’re clueless about the technology and its significance. So I’ve tried Lawnmower—cautiously, as with Acorns.

Lawnmower recently changed its system, ditching the roundup structure for a model that buys bitcoin for you once each month at a set amount you choose. And its reason for doing so is interesting: “We viewed the spare change roundups as more of a limitation,” says CFO Alex Sunnarborg. “It’s a cool and quirky thing because it’s kind of mindless, I think that’s why people like it, because setting up a budget can be really hard for people. But if you want a serious investment platform, spare change is going to be inherently low-volume. To get higher than $20 of spare change in a month, you have to swipe your card a lot. So we wanted to be a more serious investment tool for your profile.”

Of course, Sunnarborg is right—roundups can only invest so much money in a month, since they take the spare change from your credit card transactions. But that’s what makes it appealing as a safe, slow investment vehicle. After about eight months of using Lawnmower, I’ve got $65 worth of bitcoin in my Lawnmower account. Soon, the app will add the option to invest in ether, the cryptocurrency of Ethereum.