It seems a lot of Kiwis are indeed having themselves a very Merry Christmas.

That is according to new data, revealing Christmas time sees more Kiwi babies conceived than any other time of the year.

So what is the most common date for these babies to be born? Well according to Statistics New Zealand data covering births from 1980 to 2017, the most common birthdate in New Zealand is September 29.

Meaning if you were born on September 29, you share it with tens of thousands of other Kiwis, including politician Tau Henare, netball player Joline Henry, singer Jenny Morris, and countless others.

The top 10 most common birthdays in New Zealand are all between September 24 and October 4. September is also the most common month for births in several other countries including the UK, US and Australia.

After Leap Day, February 29, the least common day for births in New Zealand is December 25, Christmas Day, with Boxing Day a close second.

But it's not just about when Kiwis are getting it on - there's a deeper explanation for the trend.

Nearly 20 per cent of women giving birth in New Zealand opt for a caesarean, which means the baby will usually be born in advance. Most parents don't choose public holidays as some hospitals don't book elective caesareans on those days, and many don't want their child to have their birthday on a date that's already celebrated for something else.

The beginning of January is a less common time of year to be born, but the overall least likely month is June, with 14 of its 30 days ranked in the 300s in the list of likely dates.

It's followed by April and May - maybe the winter months of July and August aren't too popular for baby-making either.

So September and October take the (birthday) cake after all.