An $1.6 billion upgrade will see the doors of Inland Revenue (IR) closed for eight days from Thursday evening.
Only two of those days are working days - but the shutdown is making accountancy firms sweat.
"They believe that all accountants are going to go off on holiday over Easter, and that it's a great time to shut down," said Isobel Tyler from Tyler Price Accountants.
"I don't think they appreciate just how busy certain accounting firms are."
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IR's dragging us into the 21st Century by ripping up forms.
"A paper-based system costs a fortune - and this is a world where we're just increasingly moving online, right?" said managing director for Simplicity Kiwisaver Sam Stubbs.
"So having physical forms, that's old world, right? And so this will be much more efficient - much, much faster."
Tax refunds will now be automatic and online, and 1.65 million salary and wage earners will get a refund - just over a quarter of them first-timers.
On the flip-side, nearly a quarter of a million will find they owe tax - and for nearly one in three of them, it'll be a new experience.
The move will put out of business the online tax refund companies who've charged 800,000 customers for the same service.
Woohoo's the biggest to close, trumpeting its achievement as "mission accomplished".
"They push a button basically these people, and receive a refund for these people - and these people think they're wonderful because they've got them a refund," said Tyler.
"What they've never understood is they could have actually gone to the IR and got those refunds themselves."
When it comes to billing, there's good and bad news. Nearly 200,000 will be owed less than a dollar - and their refund will simply be carried over.
But the 620,000 who owe IR less than $50 will see their bills written off.