Planning to buy Christmas presents from overseas websites?

NZ Post is warning that users of its YouShop service should pay by November 20 to avoid being subject to new GST rules by the time their goods clear Customs.

Goods ordered from an off-shore e-tailer are currently not ordinarily subject to GST - as long as your purchase is less than $400.

But that's about to change.

From December 1, overseas websites whose total sales to New Zealand customers exceed $60,000 per year will be asked to add GST any purchase of $1000 to an address in NZ. Customs will be responsible for collecting GST on items worth more than $1000.

However, you won't necessarily pay more. Earlier, EY noted that imports priced $400 and $1000 will become slightly cheaper as customs duty and levies will no longer be applied to goods valued under $1000.

Revenue Minister Stuart Nash has been banking on the changes bringing in an extra $218m in tax revenue through to 2022.

EY also warned that the government might not see the anticipated bump in its coffers immediately, either, as not all overseas e-tailers will comply from the get-go.

"The government is banking on overseas suppliers to comply to raise revenue under these rules. If they don't comply, it could be a disaster from a revenue collection perspective," EY tax partner Paul Smith said.

YouShop is NZ Post's freight-forwarding service. If you sign up, NZ Post gives you an address in the US state of Oregon - which you can use for goods on Amazon.com that are not available for shipping to Kiwis. NZ Post then forwards items to your actual access in New Zealand.

Your NZ Post-allocated address in Oregon can be quite a boon if you're, say, looking to do some virtual parallel importing as well. For example, by signing up to the US version of Netflix.

In an email to YouShop customers today, NZ Post recommends paying for a YouShop delivery by November 20 to avoid being subject to the new GST regime.

It points YouShop members to IRD's broader explainer here.