Around 49,000 former and current WINZ clients who were underpaid because of a coding error will be back paid, Social Development Minister Anne Tolley says.
The error affected clients who received Accommodation Supplement payments in 1993. They were owed $29m in total.
The Ministry of Social Development (MSD) estimated the average reimbursement would be around $590.
However 48 clients would get $10,000 or more, with one retiree netting $28,500.
The error came to light after Tolley asked MSD to review its practices to ensure they were in line with legislation.