The latest Herald Election Forecast shows National edging towards a majority, but still falling short.

National is projected to win 56 seats in the next parliament, Labour 49. According to our model, a Labour-Green coalition would win 58 seats, although New Zealand First could hold the balance of power for either party.

The latest update to our forecast followed the release last night of the latest 1News Colmar Brunton poll, conducted from September 16-19. It also includes the results of a Roy Morgan poll done earlier in the month.

The Colmar Brunton poll saw a complete reversal of momentum from its previous poll a week earlier. National arrested its fall and rose six points to 46 per cent. Labour was down seven points to 37 per cent.

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According to Colmar Brunton, NZ First was back to holding the balance of power, but only by the skin of its teeth. It fell one point to 5 per cent. Any further fall would mean leader Winston Peters would have to retain the Northland seat to remain in Parliament.

National and its support partners, Act and the Maori Party, would not be able to form a government, and would need NZ First to get over the line.

The Herald's Election Forecast crunches data from every major poll conducted in the past year and the results of every election since 1999. Check out the latest update in full, and find out how it was built here.

We can't guarantee it's going to predict exactly what will happen on Saturday, but statisticians believe that collecting more data, over a longer period, is more likely to create a true picture of where New Zealand's voting intentions lie.

The data is fed into the model, which simulates thousands of outcomes. The possible outcomes give an estimate of most likely result along with lower and upper estimates.

With the Greens on the rise in recent polls, our forecast puts them well above the 5 per cent party vote threshold needed to secure seats if they don't win an electorate.

That sees that possible Labour and Green coalition projected to win 58 seats.

Our latest forecast has NZ First projected to get 6.2 per cent of the party vote and seven seats.

This is the first time the Herald model has projected NZ First getting fewer party votes than the Greens since the beginning of August, when the parties were tied together.

The polls are showing more volatility than normal due to leadership changes.

The estimates stated here are median estimates. The lower and upper estimates are shown in the visualisation and give better estimates of uncertainty surrounding the projections.

To form a government, a party or coalition needs at least 61 out of 120 seats, or to reach a confidence-and-supply agreement.

The model also includes predictions for candidates by every electorate. These are based on previous election results and take into account any polling that has taken place for a particular electorate.

There is different methodology for Epsom, which is unlike most other electorates because of tactical voting.

The visualisation also includes candidate and party vote predictions for Maori electorates. However, this is perhaps the hardest part of forecasting because of tactical voting and lack of consistent polling at electorate level.