Prime Minister John Key has shot down Winston Peters' prediction that there will be an early election next year.

The NZ First leader said on Monday the government wouldn't last a full term and would have to call an early election because it was having a bad run and had made too many mistakes.

Mr Key doesn't think so.

"I genuinely haven't made up my mind, I honestly haven't considered it," he told reporters.

"There's nothing I can see that would indicate an early election, and on the basis of that it will be in the back half of next year."

He challenged reporters to figure it out for themselves, saying he had always considered November was "a bit late" because of the APEC leaders' meeting.

"You can work out dates when there's not an All Black test match ... you can probably work it out roughly within a few weeks or a month."

The 2014 election was held on September 20.

Mr Key says he's likely to announce the date early next year.

"I personally don't think there's a huge advantage in trying to milk the date - we know we're going to have an election next year."