Minh Hung, an IT engineer, earns more than VND30 million a month.
At the outset the couple had agreed that his entire monthly income would be given to his wife to manage.
But he does not give her his bonuses or the money he earns from part-time jobs, keeping some for himself and sending some to his younger sister.
He considered financial assistance to his sister, who was in college at that time, his duty since it relieved some of the financial burden on his elderly parents.
He says he did not tell Anh about it because she dislikes his family and would have opposed it right away.
The ‘thank you’ letter her sister-in-law sent to him after graduating made the 37-year-old in Hanoi's Dong Da District furious.
"You think I'm just a scarecrow? How many secret funds do you actually have?" she raged.
Hung apologized to appease his wife though he felt he had done nothing wrong.
"Giving money to his sister without first informing me is disrespectful and that really hurt me emotionally. I lost faith in my husband as a result," she lamented.
According to a survey by American financial services CreditCards in 2021, 32 percent of coupled U.S. adults have cheated on their partners financially and 42 percent of responders said financial and physical cheating are the same.
"Spouses are afraid their partners will be unfaithful and have an affair with someone else, and which is why they secret away money," Phong Nguyen, a Hanoi psychologist,
Dr Nguyen Thi Minh, a psychology professor at the National Academy of Public Administration in HCMC, says a perfect marriage will have no financial secrets.
It is acceptable however for a spouse to have a secret fund if it does not affect the family's overall finances, he says.
"Everyone has a right to privacy, and that right must be respected as long as it does not cause any harm."
Many people mistake secret funds for private funds, resulting in unnecessary family conflicts, he says.
Hung used his money to help his parents and thus deserves praise rather than criticism, he opines.
In a 2021 survey of more than 500 readers by VnExpress, 46 percent said a spouse could have a private fund, 40 percent preferred to contribute to a common fund and keep the rest for themselves and only 14 percent believed spouses should not secret money away.
Minh Duc of Hanoi's Ha Dong District is not bothered that his wife has a ‘secret’ fund since he completely trusts and respects her.
A few days ago his wife, Nguyen Thi Ngan, complained that she had run out of money.
But when the couple and their children were watching a movie on her phone, the bank messaged to tell her it had just paid her interest and the total amount in her account had risen to VND50 million.
Duc was holding the phone when the message popped up.
He looked at his kids and said jokingly: "Mommy has a secret fund but complains about not having enough money."
Ngan blushed, grabbed her phone, and dashed to the bathroom saying "This money is for something important."
Duc responded with a loud laugh.
"I guess she might have other secret funds she keeps hidden from me, but it does not bother me," the grocery store owner says.
Duc and Ngan married when neither had money.
One time their daughter fell ill and had to go to hospital, and the medical bill was VND20 million. Duc had nowhere to turn for help, and she said, "Let me withdraw my savings."
When her husband gives her money to spend, she quietly puts away a small sum for emergency use.
She frequently complains about not having money, but always gives her husband money whenever he needs it.
"I know my wife always looks after our family, so I don't mind if she has secret funds," Duc says.
Psychologist Nguyen Thi Tam says there are people who hide money from their spouse to drink, have affairs and other nefarious purposes, and this causes marriages to fail.
One of them is Hoang Ha of Hanoi's Ba Vi District.
The 40-year-old discovered two years ago that her husband of 10 years had bought a house for and given a monthly allowance to his secret lover in HCMC.
Thanh Tung, her husband, is the director of a company who often goes on weeks-long business trips to HCMC.
Before he was caught cheating, he always showered Ha and their children with love and affection.
Two years ago a friend in HCMC spotted her husband holding a baby boy and the kid calling him "Daddy."
Ha flew to Saigon and went to an address her friend had given her, and to her shock discovered her husband was having an affair.
Tung admitted to buying a home for his lover and having children with her over the previous five years, and asked Ha for a divorce so that he could marry her.
According to Tam, an increasing number of young couples have marriage contracts to ensure financial transparency.
However, being overly focused on finances in a relationship implies a preference for money over feelings, she says.
"This is not the best option for a family."
Phong says financial harmony is only one aspect of a successful marriage.
"Without empathy and understanding, two people are simply partners, not husband and wife."
He suggests that instead of thinking of having slush funds couples should discuss how much they should contribute and jointly share financial responsibility to ensure their quality of life, allow enough space for each other and no one feels disadvantaged or overburdened.
After hearing this, Hong Anh brought her cold war with her husband to an end.
"In retrospect, he has never harmed me and has always taken care of his family properly," she says.