The automated service comes less than a week after an Auckland woman was shocked when she opened her bank account to find $12 million had been deposited by Inland Revenue.
Ms Thompson says an estimated 1.65 million New Zealanders are likely to have a refund against their name – around seven times more than the number who will receive a bill.
"Most customers will see that money deposited straight into their bank account and won't have to lift a finger.
"After receiving an assessment, we expect it will take up to two days before any refund reaches a customer's account."
Latest estimates show that around 240,000 customers can expect to receive a tax bill and that may come as a surprise to customers who haven't had one before. They will have plenty of time to pay with a due date of 7 February 2020 or they can set up an instalment arrangement.
Ms Thompson says automatic tax assessments are part of Inland Revenue's plans to make tax more straight forward.
"We expect the amount paid out annually in refunds and the number of bills to pay will decline over the coming years as we now have a system that can recognise when someone is over- or under-paying tax and can help customers correct that."