Sydney woman Clare Wainwright woke up to find herself A$24.5 million ($27.5m) richer and her mortgage paid off.
The lawyer first discovered the millions in her account on October 25.
Despite both banks being contacted about the error, the money is still in Wainwright's account.
"When NAB accidentally pays out your entire mortgage, and gives you an extra $24.5mil to redraw ... do I skip the country??" she jokingly wrote on Facebook.
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Wainwright told Fairfax Media that she had not been tempted to spend the millions.
"I'm a lawyer, which is why I haven't spent the money," she said. "Mostly because I figured it wouldn't play out that well trying to play dumb on that."
"I saw it and I thought 'Oh my gosh, it's 25 mil' and I
laughed," she said. "I showed my broker and he said 'Oh god, I'll get them to fix it'."
NAB told her broker that they would be in touch within three business days.
"They obviously don't understand I could just skip the country," she said.
Asked how she would spend $25 million, Wainwright said: "Well, if I was allowed to use it, I'd pay off my mortgage and buy another place. Or an island."