New research has found that nearly half (49%) of us are not open about our finances with our other half, while a staggering 47% don't know what their partner earns.

We all know that there are some things couples should probably never discuss: what their exes did differently, for example, or thoughts on the in-laws.

However, there are some things that it seems obvious any couple should talk about if they are financially linked through a home, a mortgage and shared bills, or if they plan to be in the future: income, outgoings and financial goals.

The study, carried out by pension advice specialist Portafina, found that many people just don’t feel able to ask their partner about their financial situation, despite one in 10 saying they thought the other has secret outgoings.

It even found that 7% of respondents admitted researching their partner’s job to try and work out what they earn rather than asking.

Jamie Smith-Thompson, managing director at Portafina said: “Money can be a sensitive subject to talk about, and the last thing you want is your financial situation to negatively impact your relationship.

“The research revealed that the secret to a happy and healthy relationship is being open and honest with your partner about everything including your finances, treating money as one, saving together and having the same goals.

“Having regular transparent discussions about your money is key to financial success as a long-term couple, and being open with each other will help create the future you both desire.”

But how important is that really? And how do you start that conversation?

[Read more: The psychology of money: Why we are rubbish at saving]

Secret debts

Personal debt can really add to the strain on couples and make it even less likely that they will feel able to discuss their finances openly with each other.

A study carried out by Prudential last year found that one in six people hides debts from their other half, with the average amount totalling more than £9,000.

Just under half of those with hidden debts said it was simply down to the cost of living.

But a secret debt burden doesn’t just jeopardise a couple’s current financial security, it could threaten their long-term stability in retirement.

Kirsty Anderson, a retirement income expert at Prudential, said: “Each year we speak to couples about money and retirement planning and each year we see large numbers of people making secret financial decisions, often assuming they’re doing what’s best for them and their partner.

“However, many of the tax benefits of pension saving are more valuable when applied to a couple’s finances as a whole, so secret money decisions could actually be having the opposite to their desired effect and jeopardising future income in retirement.

“In many cases people’s income will inevitably fall when the time comes to give up work, and the impact of repaying a secret debt when retired shouldn’t be underestimated.”

[Read more: Five money myths that could cost you]

It’s good to talk

Talking may seem impossible, but it can make a huge difference to how a couple feel about their finances – and each other.

Raymond Baxter, founder of The Relationship Blogger said: “Seven years ago, my wife and I both lost our jobs. With a small child to support, we soon burned through our savings and were forced to resort to payday loans.

“Two years later and a week before I was going to declare us both bankrupt, we had racked up over £30,000 in debt.

“We’ve just entered into an IVA (Individual Voluntary Arrangement), and I can finally breathe easily about money. I took responsibility for our money problems and it was important that I kept my wife informed every step of the way.

“Without keeping her 100% informed, and without us both holding each other accountable for our spending habits, I hate to think where we would be today.”

The other side of the coin

What would be worse: discovering your partner had secret debts or discovering they had a secret escape fund?

It makes good financial sense to have emergency savings but a couple of years ago the Money Advice Service carried out research that showed one in 10 married adults in the UK have a secret stash of cash in case they need to get out of the relationship in a hurry.

The average ‘escape fund’ was around £7,500.

Why is it so hard to talk about money?

If you can discuss sex with your partner then you can surely talk about money, right? Well, wrong, apparently.

Corinne Sweet, psychologist, psychotherapist and author of Stop Fighting About Money, says that talking about finances evokes feelings of vulnerability and dependency.

She says: “Many couples hide their true money status as they need to control the power in the relationship. Having money secrets, or a secret escape stash, is likely a way of showing that you have doubts about the relationship.

“It is fairly essential to get your ‘money baggage’ out in the open at the start of the relationship, and try and clear up any nasty (or nice) surprises as you go along as secrecy can eat away at the infrastructure of a relationship.”

Here are Corinne’s top tips for talking more about money:

  • Strive to voice your beliefs about money as early on in the relationship as you can, to avoid misunderstandings building up;
  • If you are secretive about money, ask yourself why? Are you protecting yourself? What is it you don’t trust in your partner?;
  • Relationships need some mutually agreed ground rules about money – these can be re-negotiated as you go along;
  • If you have unequal incomes or assets, try and work out ways of paying for things that reflect this: for example a 70/30 or a 60/40 split;
  • If you have debts, try and be honest about it (at least with yourself). Take full responsibility for clearing them and keep on top of them.

Whether it’s debt or savings, it seems that we’re a secretive nation, even with our partners.

But talking about how much we actually earn might be a good start to a bigger, even more important conversation.

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