For more than 70 years, the first Monday of June was known as Queen's Birthday. This year, New Zealand will be celebrating the King's Birthday on Monday 3 June.

Although the day goes by a different name, the rules are much the same. Just like the Queen's Birthday, the public holiday is a non-working day.

That means if you're working on the day (as regularly rostered), you're entitled to time-and-a-half pay and an alternative day off.

What's open?

Trading restrictions don't apply to King's Birthday in the way they would for Easter holidays, Christmas, or the first half of Anzac Day.

Shops, restaurants, cafes and other hospitality and retail venues will be open as usual, but they can choose to close if they wish - so it pays to check opening hours beforehand.

Supermarkets and malls will be open too, but some may operate with shorter hours.

Surcharges

Public holidays are an expensive day to be a business and King's Birthday is no different.

Hospitality businesses in particular may add a 15 percent surcharge to their services - this is usually to cover the costs of paying employees time-and-a-half.

If a business does charge a surcharge, they must have clear signage communicating this to the customer.

This can be done with the display of signs detailing the surcharge, a message on the business's website, or by verbally letting the customer know at the time of purchase or before they order.

If customers believe they have been misled about a surcharge, they can complain to the Commerce Commission.

Why do we celebrate the King's Birthday in June?

Although King Charles III's birthday falls later in the year, New Zealand still marks the monarch's birthday in June.

King Charles will officially celebrate his 76th birthday on 14 November, but now that he has taken the throne, he receives the privilege of celebrating his birthday twice every year.

It was the same with Queen Elizabeth, whose real birthday was on 21 April.

The reason? Britain's winter weather.

It's traditional for British monarchs who are not born in summer to celebrate twice, with a second official birthday. Once on their actual date of birth, and then later in the British summer with a grand parade.

The tradition was started by George II in 1748, who also had a November birthday, and deemed it too cold for a celebratory parade.

-RNZ.