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.
Wainwright told Fairfax Media that she had not been tempted to spend the millions.