"You spent HOW MUCH on that clapped-out old rustbucket?"

Hell hath no fury like a woman left out of a major financial decision.

Researchers consistently find that it's arguments over money, rather than romance or who gets to walk the dog, that often leads to relationship breakdown.

A Kiwi study by Relationships Aotearoa found four in 10 couples quarrel over money and financial security.

And it makes no difference whether you're a Rich Lister power couple or just scraping by; bickering about bills kills romance faster than you can say "divorce lawyer".

If you want to keep both your finances and your relationship intact, watch out for these common traps.

UNILATERAL DECISION-MAKING

There was a time when a man's weekly pay packet was deposited straight into the outstretched hand of his thrifty wife, but those days are gone. Well, mostly.

Family Law Results principal Selina Trigg deals with relationships all the time, many in various states of decay, so she knows how the cracks form.

One of the re-occurring problems is a financial power imbalance, and it's often women who are vulnerable.

"For some of my female clients, they have felt that they've been in a situation where the finances have been controlled, and it's been indicative of a bigger power issue," she says.

It's not always simple. The person viewed as "controlling" may simply be trying to exercise some financial prudence and keep a lid on spending.

Then there's the fact that one person might call the shots simply because they're better equipped to so, or because their partner is allergic to book-keeping.

Whoever takes the role, make sure it's mutually agreed upon.

I'M RIGHT, YOU'RE WRONG

You've got a real humdinger of a business idea. The road to riches is as simple as throwing in the towel at your boring day job and re-financing the house. Wait - why doesn't the missus look impressed?

"A big part of what I do when I work with couples is relationship counselling," says financial planner and author Liz Koh.

She's joking ... sort of. Koh says everyone has a different "money personality", and when they clash, sparks fly. You might be a hoarder, a big spender, a risk-taker or an entrepreneur, but chances are your partner isn't.

"Quite often it'll start to show up any cracks in a relationship," says Koh. The real acid test is whether you can find a middle ground.

She remembers one security-conscious client who was dead set on saving every penny towards retirement, but his wife was hanging out for a shiny new kitchen.

The tension between the pair was only resolved when Koh mapped out a plan that showed the two goals weren't mutually exclusive.

"Where you see things go wrong in a relationship is one person will be attempting to tell the other person that they're wrong," she says. "There is no right and wrong."

Handled well with clear communication, conflicting money personalities actually complement each other. Conservative worry-warts have their place. Imagine the perils of two carefree risk-takers feeding off each other.

"They'll be on a huge rollercoaster ride where they could make a fortune - and lose it!" says Koh.

DIVIDED WE FALL

Once you've shacked up with someone, your finances inevitably begin to blur to some degree. The obvious pre-emptive strike against any money problems is to keep your money separated, with no joint accounts or credit cards.

But that becomes pretty impractical for bill payments and the like, and it hardly seems conducive to building a relationship.

"Where that gets entrenched it can become a bit of a problem, because you need to have those shared goals," says Koh.

"If you're managing your money separately, it can be a little bit harder to do that."

KEEPING SECRETS

Skulking around spending household money behind your partner's back is a fast track to relationship counselling. Anniversary presents are the exception.

The worst manifestation is problem gambling, which is something that Relationships Services Manukau clinical manager Georgina Wilkinson comes up against all the time:

"They've been asked to pay the power bill, and the power bill's not paid. There's arguing, there's fighting, she's drinking."

Wilkinson refers these couples on to the Problem Gambling Foundation. But the same trust and resentment issues apply equally to other forms of secret spending.

"Some mums feel they deserve something extra spent on them, and so they'll do it without consulting their husband or their partner," she says.

The pattern she sees all too often is financial stress leading to arguments, then alcohol, then violence. It's always better to keep everything above board and on the level.

NAIVETY

The power of love endures forever ... in Disney cartoons.

"I think that if you're in a second relationship, you've probably been well and truly disavowed of that view," says Trigg.

"None of my clients have ever said 'when I was walking up the aisle, I knew it wasn't going to last'."

Let's be honest. Most relationships will fall over, and even the holy union of marriage has a one in three strike-out rate.

While it's not ideal to keep all your money separated, writing a pre-nup agreement is a sensible precaution when there's an imbalance in assets.

That applies equally to marriage or de facto couples, both subject to the Property (Relationships) Act.

There's ways and means of dealing with it, though. The "sign it or we're done" style has scuttled more than one relationship before it began.

Trigg says about half of couples take the hardline contracting out: "What's mine is mine, and you're never getting your hands on it."

Others ringfence their assets at their current value, and recognise shared effort by splitting any future improvements.

"It's quite a different philosophical underpinning," she says.

AFTERMATH

If a relationship does fall to pieces, you better pick up all the shards or you'll end up with one jammed in your foot.

The Banking Ombudsman warns that banks will keep joint accounts or credit cards open to withdraw money or take on debt, as per normal, if they're not told.

Both parties have to be contacted to settle the account, but if you can't hash it out then at least let the bank know, because they can freeze the funds.

"To avoid further debt being incurred, the safest course is to ask the bank to suspend the credit card account," says the Ombudsman's guide.

A search for "joint account" returns 237 hits on the Banking Ombudsman's website, and trawling through the tales of woe and financial ruin is a sobering read.

Take Ms M and Mr P. Their break up was relatively amicable, so they left a joint account open as "either to sign" while Ms M dealt with other property.

But Mr P secretly withdrew $10,000 from the account, and the bank authorised it.

At first Ms M tried to blame the bank, but eventually accepted that she would probably have to haul her ex through the courts to recover the money.

All of which goes to show that relationships are a potential minefield when it comes to your finances. Tread with caution.

- © Fairfax NZ News