Obesity is costing New Zealand between $722 million and $849 million a year, an Auckland University study says.
The study showed up to 4.4 per cent of New Zealand's healthcare costs, an estimated $624 million, was spent on obesity.
In addition, there were costs of between $98 million and $225 million for lost productivity from obesity through absenteeism, premature death, or recruitment and training of replacement staff.
"These figures represent a major drain on health resources and point to a need to increase efforts on prevention," said Professor Boyd Swinburn from the university's school of population health.
The costs didn't include foregone taxes, costs of disability and loss of well-being.
The report says about 35 per cent of New Zealanders over 15 are overweight, while 25.4 per cent are obese.
Obesity is a key risk factor for illnesses such as cardiovascular disease, type 2 diabetes and some cancers.
The study is based on figures from 2006, the university said.
An earlier study estimated the healthcare costs of obesity in New Zealand based on 1991 figures was $135 million.