ANZ is making a claim on behalf of impacted KiwiSaver members to Inland Revenue for the additional member tax credits to be credited to those customers’ KiwiSaver accounts.

Those affected are people who have been members since 2009.

In addition, ANZ will credit their KiwiSaver accounts with the investment returns that would put them in at least the same position they would have been if the error had not occurred. ANZ expects payments to be completed in August.

While ANZ has identified 51,000 customers who are financially impacted by the error, the bank said exact numbers and amounts would not be known until the correction had been processed by Inland Revenue.

For most of those impacted members the underpaid amounts are expected to be $50 or less.

Spokesman Stefan Herrick said the problem arose because the start date of some KiwiSaver members was set as their actual joining date, instead of the first day of that month. "This meant their pro-rata MTC amount was slightly underestimated for that year. All subsequent years were correct."

For a number of other members who switched to ANZ from other providers, their MTC was based on the time they were in an ANZ scheme only.  A one-off processing error in 2009 involved a small number of members who made a voluntary contribution by direct debit to their KiwiSaver account. The money went into their account, but that contribution was not included in the calculation of the MTC for that year.