This is the most important money move that women aren't making

Recently, I invited some friends to my apartment to talk about money and I was surprised — and a bit alarmed — to learn that roughly half the group weren't investing their money. Not in a 401(k) or a Roth IRA or a robo-advisor. Not a single dollar. 

It can be hard to be friends with a personal finance reporter — I was so tempted to pull out my phone, bring up compound interest charts and lecture these smart women on how important it is to start investing in your 20s, which I'm guessing isn't exactly their definition of a good time.

But my heart is in the right place: I want my friends to lead successful, prosperous lives. And that makes it hard to hold my tongue when people I love are making what I consider to be a serious mistake. 

Money talk is delicate. I don't want to come across as overbearing and condescending or out of touch with their financial realities. As easy as it is for me to tell people they should be investing, the reality is it can be a scary prospect for young people who already have so many other financial obligations.

And it isn't always easy to change their preconceived notions of what investing is and why it's important. Investing makes me feel more secure, but some of the people I know relate it to gambling; they're more comfortable keeping their savings in cash. Others say they'll start investing when they earn more.  

Women are now better educated than men and outnumber them in the workforce. Many of my friends painstakingly plan their careers, write out where they see themselves in five, 10, 20 years and consider themselves independent-minded feminists. Yet the care and planning they put into virtually every part of their lives doesn't always extended to their money — especially their investments.

That's a point Sallie Krawcheck, CEO of the investing platform Ellevest, drives home again and again.

"If we're not investing, we're doing most of the hard work around money (you know, going to work every day, turning in that amazing design, landing the difficult-to-close client, beating our sales projections)….but we're only getting about half the reward," Krawcheck writes on her company's blog. "We're depriving ourselves of the ability to take on more risks in our career, to 'play loose,' to have more fun in what we do, to do more in our careers, if we don't have a financial cushion built up."

It's not only 20-something women who aren't investing. Less than 70% of U.S. women are investing money for retirement, according to the TransAmerica Center for Retirement Studies, compared to 81% of men. Of those who are investing, the median household retirement savings for women is just $23,000, compared to $76,000 among men, TransAmerica found.

Coupled with the gender wage gap, and the fact that women are more likely to leave the workforce, at least temporarily, to provide unpaid care for children or other family members, women are worse off than men on almost every investing and retirement metric you can find. One hopeful note, however, is that when women do invest, they often earn higher returns than men, studies have found.

Women place investing for retirement as their fifth most important financial priority, after meeting daily living costs, meeting debt obligations, paying for housing and general savings, according to a 2018 report from insurance brokerage Willis Towers Watson. For men, investing for retirement is No. 1. 

There are, of course, real structural and societal reasons for this disconnect in financial priorities. As mentioned above, women still take on most of the caregiving duties and, on average, have less money to work with than men. Women also carry more debt than men, and their earnings peak 10 years earlier.

All of these are valid reasons why investing might take a backseat to other priorities. At the same time, these stats are what drives me to make investing a priority, above certain other goals I might have.

Investing in index funds, which most financial professionals advise as a smart long-term strategy, is one of the few ways women have to build real wealth, to ensure that we have sufficient funds to fall back on, to be truly financially independent one day. It requires sacrifice, but the reality is, it's a necessity in the world we live in.

Only 24% of women surveyed by Fidelity Investments in 2018 said they were comfortable with how much they knew about investing. But there's no secret information women need to unlock in order to invest. Knowing the basics — invest consistently in low-cost funds that cover an array of companies and sectors, for a long time — is enough to get in the market, especially if you have decades until retirement.

One of the most important things I try to remind my friends is that you don't need thousands, or even hundreds, of dollars to get started investing. If you have access to a 401(k) at work, then you can invest with as little as 1% of your paycheck each month, though ideally you'll contribute at least up to any employer match you might be offered.

You can also open an IRA or brokerage account via an app like Ellevest, Wealthfront or Betterment and start by contributing small sums of money — as little as $1 to $10 a month in many cases. Plus, setting up an account and transferring funds into investments can take as little as 15 minutes.

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Here are a few more things to keep in mind as you get started.

Investing is the most valuable thing women can do, Krawcheck writes on her company's blog.

While it's never bad to have a chunk of money set aside in a savings account, it can be detrimental to your long-term financial health if you're not also investing and earning higher returns on your money. Nationally, savings accounts earn 0.09% interest on average, while you can find some higher yield options around 2%. On the flip side, the S&P 500 has long-term average returns over 9%.

Krawcheck says those lost returns are "a bigger drain" on a woman's net worth than the wage gap.

"[Women] tend to leave more than 70% of our wealth in cash as opposed to investing it," Krawcheck previously told CNBC Make It. "For the typical professional woman, that can cost her hundreds of thousands — for some women, millions — of dollars over the course of their lives."

Yes, your investments will experience increases and decreases as the market fluctuates and movements can often be dramatic. But investing for retirement is a long-term strategy. You're not looking to flip them to make a quick buck. Instead, you want to build wealth over decades.

You don't need a ton of money to start investing, but you do want to regularly contribute to your account. And research shows that workers — especially low-wage workers — who automate their investments have more money saved and invested over the long term than those who don't.

Automating your investments will ensure you not only keep building your balances, but that you are investing no matter what the stock market is doing. 

A 401(k) is an easy place to start with automation: You simply pick a percentage of your paycheck to contribute to your account each pay period. It's automatically transferred and you don't even get a chance to really miss the money. You can also sign up for an individual retirement account, such as a Roth IRA, and connect your bank account to it, so that funds are regularly transferred.

The saying goes that the best time to start investing was yesterday. The second-best time is today. The earlier you start, the more time your investments have to compound, or earn returns not just on your principal balance, but on other returns. That will help your wealth grow so you can save hundreds of thousands or even millions of dollars.

"A dollar invested in your 20s is worth more than a dollar invested in your 30s is worth more than a dollar invested in your 40s is worth much more than in your 50s, 60s or 70s," Krawcheck previously told CNBC Make It.

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Disclosure: NBCUniversal and Comcast Ventures are investors in Acorns.