More than 52,000 people were overpaid superannuation or veteran pensions in the last financial year, 50 percent more than five years ago.
In the 12 months to June 2017, 52,525 people receiving either New Zealand superannuation or a veteran's pension were found to have been overpaid, Ministry of Social Development (MSD) figures released to RNZ show.
That compares to 35,101 cases of overpayment discovered in 2013.
The ministry did not say how much in total was overpaid each year but said the average in 2017 was $625, while the single largest overpaid amount was $207,139.
In August New Zealand First leader Winston Peters said he had received a superannuation overpayment and had paid back the money. He did not disclose the amount.
The ministry said one of the factors in overpayments related to clients who were also receiving a foreign pension.
"When a person is in receipt of New Zealand Superannuation, they have an obligation to inform the ministry of any changes that may affect their entitlement.
"Where this doesn't happen clients can incur an overpayment resulting in a debt to be repaid," an MSD statement said.
Just nine people had been prosecuted for overpayments of NZ Super between 2014 and 2017, it said. There were no prosecutions involving veteran pensions.
MSD said there are about 700,000 pensioners in New Zealand