Experts advise people to “never keep secrets in a relationship” yet, according to Fidelity Investments 2015 Couples Retirement Study, 43 percent of today’s couples cannot correctly estimate how much their spouse earns.

John Sweeney, Fidelity Investments Executive Vice President, Retirement Income and Investment Insights spoke with Benzinga about the study’s findings and how couples can minimize the money mysteries between them.

Related: Fidelity Investments VP Ken Hevert Shares Retirement Tips At Tax Time

Benzinga: The results of this study are fascinating, to say the least. Just how surprised were you that 43 percent of couples could not correctly identify what their significant other earns?

John Sweeney:  We were very surprised. Particularly, we asked folks, "Do you communicate well about financial issues?" Two-thirds of them said, "Yes, we do."

Then, when we asked the specific question, "What does your partner bring home?" to see that 43 percent couldn't correctly identify what their partner made that was surprising to us.

BZ:  Why do you suppose that is?

JS:  A couple things. One is certainly a reluctance to share personal financial information with anybody. We're brought up not to ask people what they make, and it's an issue that reflects how the marketplace values our skills and our services.

We also found two other factors that weigh in here.

One is we have people moving toward a more project-based economy. What that means is I work on a project. It may be in construction where I work for a period and at the end of that project, I may roll off and have to find another project.

I may find one immediately, or may have a gap in my employment where I'm looking for work for a month or two. This makes it difficult for people to predict their own income year to year.

The second factor is the stock market. We're in year six of a bull run on the stock market. People who rely on the markets for parts of their income for stock option compensation or are retired and living somewhat off securities may have had more income over the past few years due to the positive stock market than going forward.

BZ:  What other kinds of things do people have difficulty discussing in terms of finances?

JS:  We see different factors for people of different ages.

For young investors, it's really being aligned around particular goals that you have in the near term.

Do we want to build a house together? Do we want to have children and pay for their college? How do we think about saving for retirement when it's so far off into the future? It's really something you defer worrying about in favor of short-term goals and short-term needs.

For folks closer to retirement, they want to be aligned on what that retirement life looks like together. Do you want to live closer to the grandkids? Do you want to live in your current home, or downsize? Do you want to live in a retirement-oriented community? 

Being aligned around what lifestyle looks like in retirement is an important precursor to figuring out what it's going to cost. If you want to travel the world, you'd better have a budget that can sustain that. If you're comfortable staying at home in a house that you've paid off, then you need much less income.

BZ:  These are important conversations to be had. What’s the first step?

JS:  I think the important place to start is budget. You want to be aligned on how much you're spending considering how much you're bringing home.

As we offer advice to folks, we say, solve for the goals first, and then figure out how to live on what's left.

BZ:  Can you give an example?

JS:  If I talk to a 22-year-old starting out in their first job, and they say, "I can't possibly save for my 401(k) because I have to pay for student loans, I need a car to get to my job, I need to pay for a home," those are (actually) all good reasons to save.

We would say take 15 percent of what you make, put it in a 401(k) or individual retirement account and figure out how to live on what's left.

If I offered you your current job at 85 percent of what you currently make, would you keep it? 

The question is, how do I save off the top, and how do I learn to budget what's left?

BZ:  What are some tips for helping people get started?

JS:  We talk about three things - communication, collaboration and control.

Communication is being aligned on, "What are our goals that we share together, how do we want our life together to look going into the future?"

The second part is collaborate. We have to work this out together. We have to be aligned around those goals.

The third part is really around control. That's a bit of budgeting and monitoring, making sure that you set up a budget.

If you're paying yourself off the top first, worrying about whether you went to the movies or dined out a few more times this month versus last month is less important as long as you've established that savings trajectory across the top.

Related: 9 IRA FAQs: Invest In Yourself, Educate Yourself

BZ:  What about people who are looking for a little more help?

JS:  We have many resources available at fidelity.com.

We have a couple's quiz that's a great way to break the ice. You go through nine questions. You email the quiz to your spouse or partner. He or she goes through those same nine questions, and then you have the ability to compare and contrast answers and see where you have commonalities and differences.

We also have a newsletter called Viewpoints, which comes out weekly and offers tips on the markets, investing ideas and personal finance.

At the time of this writing, Jim Probasco  had no position in any mentioned securities.