Nearly one in five Kiwis has hidden savings or debt from their other half and women are the bigger culprits.
Research by credit rating agency Credit Simple has found almost 18 per cent of people admitted to having money or debt their partner isn't aware of.
Credit Simple New Zealand boss Hazel Phillips said its research didn't delve into why people kept secret accounts because there could be so many reasons.
But she said women were far more likely to have secret savings or debt and it also tended to be younger women.
Nearly two-thirds of those with a hidden account were women compared to men at 36 per cent.
Phillips said one reason could be because women were trying to protect themselves, particularly if they were in a new relationship.
The research also found 28 per cent of people said they had been burned financially by a partner and 64 per cent of those burned were women.
The most common examples included New Zealanders who racked up secret credit card debt, partners who refused to pay their share of debt after a relationship ended, partners who said they were paying bills but weren't, and even those who forged their partner's signature on loan documents
Philips said one way people could protect themselves was to check their credit score before entering into a new relationship and then keep checking it once in the relationship.
A new service on the website also allowed people to check all the different accounts that were open in their name.
"So if someone takes out something in your name you didn't know about, it will come up," she said.
It is free to check your credit score on the website and does not register as a mark against your credit account meaning people can check their own details as many times as they want.
Phillips said before the research she had thought any money secrets were likely to be low level - like a pair of new shoes bought and then hidden in a wardrobe.
"But it is actually fairly grunty stuff," she said.
The majority of people keeping finances secret from their partner were hiding private bank accounts or cash reserves (67.3 per cent), while almost 18 per cent had secret debt.
The research did not ask people how much savings or debt they kept hidden.