Rugby New Zealand 2011, a joint venture between the New Zealand government and the New Zealand Rugby Union, had expected losses closer to NZ$40 million.
In the run-up to the World Cup, organisers had to contend with the impact of the global financial crisis as well as the deadly Christchurch earthquake, which forced the switching of seven matches less than six months before the event.
The NZRU will cover NZ$10 million of the loss with the balance coming from the public purse.
World Cup minister Murray McCully said the country would, however, continue to benefit economically from successfully hosting rugby's showpiece event for years to come.
"We welcomed 133,000 visitors to our shores and we were superb hosts for a great six-week celebration," he said in a statement.
"The huge television audiences and extensive media coverage generated by the tournament boosted our international profile.
"We also forged valuable new business partnerships and showed the world we are a smart and innovative economy capable of delivering major global events.
"We made the most of being in the world's spotlight, so this result really is the icing on the cake."
New Zealand delighted their home fans by beating France in the final to win the tournament which will next be held in England in 2015, while Japan will be Asia's first hosts four years later.