What a sneaky lot you are. Running secret slush funds on the side from the joint account, telling the other half you're paying more into the mortgage only to redraw it ...

But don't think you'll get away with it.

"Money is one of the top three reasons for a partnership breakdown," the senior manager of clinical services at Relationships Australia, Gail Westcott, says.

Often couples are loath to talk about finances with each other yet it's no holds barred over who cleans the shower.

"If you take the leap of faith to live with someone then you should take the leap of faith in being transparent with your finances," the managing director of BFG Financial Services, Suzanne Haddan, says.

"Know what each of you has and your expectations. And do a budget. Everybody tries to duck and weave over a budget because they think it's boring," she adds.

All right, it is. But once you have a budget you can set financial goals, such as saving for a house, and have a far greater chance of getting there.

"Otherwise you'll be aimless," Haddan says. "A goal must be measurable and have a time frame. Those under 35 typically don't sit down and say, 'what happens if one of us gets sick?'"

SHARE THE LOAD

Surprisingly, another no-no is one partner doing the finances.

Sounds natural considering rarely are both people equally interested in budgeting, not to mention one being more of a spendthrift than the other. No names, no pack drill but I think you know who I mean.

Sometimes it's a power trip, but just as often it's simply the result of one partner being too busy. Or not being all that interested in money - managing it, that is.

"There's friction if one isn't as frugal as the other," Haddan says. "That creates a lot of stress."

If things go wrong when there's an unequal approach to managing money, it compounds the stress.

The one who got the pair in a fix suffers, but so does the other partner who then can't understand how they got into the predicament in the first place.

When Paul Moran of Paul Moran Financial Planning sees a young couple, he's blunt. "They'll come in for a financial plan and talk about negative gearing," he says.

"So I ask, 'When are you going to have a family?' They look sheepish and talk in generalities. But that's when they'll be locked in one income and things can go badly."

Many financial planners recommend young couples sign a pre-nup, officially a binding financial agreement. But Moran has a slightly different take, suggesting a sunset clause.

"You only need it if there's a significant asset imbalance at the start," he says. "Even then, I suggest it stops after a period. After 10 years all bets are off."

Besides, binding financial agreements are not always, uh, binding. Unlike a commercial contract, it depends whether any kind of duress was involved or how circumstances might have since changed.

When it's drawn up, "it's hard to see what's going to happen in the future, such as whether there will be children or illness", says Geoff Sinclair, family law section chairman of the Law Council of Australia.

"If it's ambiguous or not perfect, it can be struck down."

Even one partner claiming not to have been told everything can cancel the agreement.

In fact, "most lawyers in Sydney are refusing to do them and Melbourne is starting to back out", Sinclair says.

BANK TOGETHER, STAY TOGETHER

Quaint as it sounds, the best money move a young couple can make is a joint bank account.

"Financial management is easier as a team," Haddan says.

By the way, that's not necessarily true for those on their second (or later) round, but I'm coming to you.

The trick is that all income goes into it, but some is allocated to each partner as sort of marital pocket money.

"There's a core account for core expenses. Everything goes into that, then comes out rather than the other way around," Moran says.

"I'm a big fan of having multiple bank accounts - sub-accounts for the mortgage, bills and food. That forces you to stick to your budget. And each partner should have their own slush fund for things like presents."

Oh, doing that already? Good, but each has to know what the other is getting, though how you spend it is your business.

Which brings me back to the B-word. Whatever your age, you need a budget.

"Sitting down and doing a budget is important, especially when there's a mismatch between what each spends," Moran says.

"When you look at what you spend, you find you don't have as much as you think. You spend small amounts more frequently."

Also, couples "spend way too much on housing", which finishes up in more debt, Moran says.

GET OFF THE TREADMILL

Oddly enough, couples on higher incomes have their own form of financial stress.

They feel they have to keep up with a lifestyle - private education, overseas holidays and the like - that "can cause a great deal of stress for the male", says Tricia Peters, a divorce financial planner - yes, a sign of the times - at the Melbourne Collaborative Alliance.

It's not so much a jealous keeping up with the Joneses as fitting in at a dinner party at the Browns.

"As the kids get older they get more expensive. So you live on the equity of the house through a line of credit.

"The sad thing is the guys here know that's the case and have tried to keep up appearances and when the marriage breaks up the women don't understand why they can't have the things they had," she says.

For those in a second marriage, estate planning is more critical, so having assets in separate names makes more sense.

FINANCIAL DANGER SIGNS

Bickering.

Separate bank accounts unknown to the other.

Using the credit card to pay bills.

Conflicting savings goals.

Disagreement on how income is divvied up.

A partner opens a credit card without telling the other.

A partner buys something expensive without telling the other.

Woman stays at home to have a baby and feels financially disempowered.

Signing a loan document in the partner's name.

Spending suddenly increases.

TIPS TO HOLD IT TOGETHER

Here are some of Westcott's tips for matrimonial and monetary harmony:

Talk about finances at a neutral time - not when somebody is rushed or stressed.

Give a little to get a little - that means sharing.

Discuss how your parents handled money.

Track your spending.

Agree to disagree sometimes.

Allow yourself some pocket money so you don't feel trapped by a financial plan.

Designate a bill payer and swap, say, every three months.

If all else fails, ask a third party to help.

- Sydney Morning Herald