Among the major life milestones, marriage is one of the most profound when it comes to its impact on your finances. True, becoming a parent may feel heavier because kids are so expensive -- but you get to decide most money questions for them. But a spouse? They're your partner -- a partner who comes with their own baggage, ideas, debts, assets, and lifestyle, which you have to adapt to. And vice versa, of course.

In this segment of the Motley Fool Answers podcast, co-hosts Alison Southwick and Robert Brokamp have brought in a special guest -- recently married financial planner Sean Gates -- to talk about the mistakes that couples frequently fall into. These aren't deceptive problems like hiding assets or concealing spending, either. They're problems you can create by doing things with the best of intentions.

A full transcript follows the video.

This video was recorded on Feb. 11, 2019.

Alison Southwick: Let's move on to some mistakes that maybe you have experienced or maybe in your experience as a financial planner have noticed other people often making.

Sean Gates: The first one is letting one person in the relationship be the "finance" person. This I run into all the time where I'll be speaking to folks who are going to retire. Let's say they're retired and they're now 20 years into retirement. I'll get a call from the "finance" person and they'll say, "I haven't needed a money manager in the past because I've been dealing with the finances, but now I'm worried that I'm going to die and my wife or husband won't know what to do."

I'm like, "Well, that's not an ideal position to find yourself in. Your partner should know more about the finances that you don't need to hire a third party to get abreast of the situation. You still might be warranted to have a manager involved, but you don't want to just throw this on someone else and have them have to talk to a third party to get that information." I think keeping each other honest in the finances is important.

Robert Brokamp: We recently had some family friends in their 80s. The husband handled all the money, had a stroke, and the wife is just totally lost. Doesn't know how to write checks. Doesn't even know where to find the checks. Doesn't know how to put gas in the car because that was something the husband always did. She's totally lost and he's not in any capacity to help her. So certainly it would have been much better for her to be more involved before this point.

Gates: I would say one further knock-on effect, there, is that sometimes the parents will assume that the kids will step in and help, but a lot of the times the kids are worse off than the parents in terms of knowledge of finances because families typically don't talk about finances or they have a completely different idea of what the money should do for the familial wealth. I think as a couple, you should be cohesive about it early on and as quickly as you can.

Southwick: Bro, didn't you used to do the "State of the Union" address for your family?

Brokamp: Yes.

Southwick: How do you recommend they go about staying on the same page?

Gates: Something like an annual check-in. In financial planning you'll do quarterly or annual check-ins with the clients. I think very similarly with husband and wife just have a time-based system where you review your finances together and you just talk about everything that happened over the course of the year.

Brokamp: Way back when, in 2000, both my wife and I worked at The Fool, and we co-wrote an article called, A Couple's Financial Manifesto, and it was one of the most popular articles for that year. I went back and read it recently, because this was quite a while ago, and we were doing it monthly.

We don't do it anymore, because we have a pretty good sense of each other's financial habits and what our priorities are but doing that in the beginning is very helpful.

Gates: And I think as you go through that process, a more frequent check-in is probably going to help build the processes in place and then you can fall off and go slower.

Southwick: What's another mistake to avoid?

Gates: The other mistake that I see people make is [this might be more generational] but combining finances too aggressively. One of the things that I hear most frequently when I'm talking with married couples is that one of the things from a financial perspective that has benefited their peace of mind and comfort with one another is having some sort of selfish budget, where there's $1,000 that they're not necessarily going to account for, for the month that they can spend on whatever they want. That way you don't have to get permission from your spouse or partner to go spend on something that you want. I think that's a really nice feature to have.

Southwick: And one last mistake?

Gates: This one is a little bit controversial, as well, but this would be letting the more emotional person be the finance person. In my experience -- and I've been doing this for 10-plus years now -- men in the relationship tend to be the investment managers. They control the retirement accounts, the stock picking, and all of that stuff. Women tend to control the day-to-day finances. They'll do the budgeting. What are we going to spend this month? It's not always, but this is a commonality that I've seen.

And what's also true, anecdotally, is that men tend to be more emotional with money. Men are often worse at the investment side of the equation. So I sometimes will recommend to folks that they consider flipping roles. What's nice about this is that the other partner can learn the skill set of the other. It's just getting that education.

But there's actually good research. Fidelity did a fairly massive study where it showed that women tended to outperform men with their accounts by about 0.4, so about 40 basis points. It doesn't sound like a lot, but over time compounded it can be quite significant. It's just a good thing to try and make sure that the right person is doing the right job for your family.

Southwick: We found in our relationship that I do have a better track record, mostly because I don't fiddle with it.

Gates: Exactly.

Southwick: I buy stuff and then I don't come back ever again, whereas Ron likes to fiddle with it. He likes to buy and sell and buy and sell. When I say buy and sell, I mean six months later or maybe a year later, whereas I'm still holding onto the very first stocks I ever bought like seven years ago. He has a love of it as a hobbyist investor that I don't, which is where I probably get my outperformance.

Gates: There's a number of ways that you could look at it. Another way is that women tend to be more self-aware of what they don't know. Where their expertise lies. Whereas men tend to be more overconfident. I'm sure people will take offense to some of this, but I think that leads to your point, which is that you don't claim to be an expert on investing, so you're just going to invest normally. Invest in the index funds, the common wisdom, and then just forget about it and you'll end up doing better.

Brokamp: Coincidentally, CreditCard.com just released its latest financial infidelity poll and one of the findings is that 44% of those who are living with a romantic partner believe they're better money managers than their partners, whereas 12% think they're worse. Men are more likely to say they're better at it. That they're better than their partners and women more likely to say they're worse. Men are definitely more confident about money.

For other fun facts, 19% of U.S. adults who are in some sort of live-in relationship [that's 29 million people] are hiding some sort of a checking, savings, or credit card account.

Southwick: 19% of people are hiding money from their...

Brokamp: Yup. And 20% of all the survey respondents feel that a partner hiding a secret bank account is worse than physically cheating, 45% disagree that it's worse, and 35% feel it's about the same.

Southwick: It's not great!

Brokamp: It's not great!

Southwick: It's not good!

Brokamp: It's not great! Millennials apparently are the sneakiest. They're twice as likely to be hiding money than everyone else.

Gates: I have six hidden checking accounts.

Southwick: Checking! So boring!

Gates: I'm good at it.

Southwick: I just love to write checks! You talked already about some recommendations for trackers going through and looking at your spending. What other recommendations do you have for our listeners for other resources?

Gates: It sounds like Bro has set me up with...

Brokamp: The Fooly Wed Game.

Gates: The Fooly Wed Game. That sounds awesome! Actually, I was trying to prepare for this podcast and there aren't a ton of great resources for this, especially online. There's usually just message boards and things like that which are hard to get to the heart of the issue.

There are a couple of good books that I would recommend. One that is recommended by a colleague of ours, Chris Harris, that he'll set up with newlyweds is called Prenups for Lovers book.

Brokamp: Prenuptials for lovers!

Southwick: Do you have it pulled up so you can see the subtitle? The subtitle is, A Romantic Guide to Prenuptial Agreements. That's a pretty awesome title!

Gates: When I polled people, I got quite a few hits for that. I think that one's good. Then I found another one that I thought was relevant. It's actually written by some attorneys. It's called, I Do, You Do... but Just Sign Here. This book is a little bit more specific, because it talks about both prenuptials and postnuptials which, again, you should pay attention to postnuptials because I think there's a taboo around prenuptials and it's not an irrevocable decision. If you don't have a prenuptial, you're not screwed.