The latest update to the Herald election forecast reinforces the prediction that we're in for a tight race.

Both Labour and National are projected to win around 51 seats in the poll on September 23.

The model incorporates the most recently released poll, the Newshub Reid Research survey which took place from August 22-30. An earlier version of our forecast already factored in the One News Colmar Brunton poll, which took place from August 26-30.

Check out the latest update and find out how the model was built here.

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As the two major parties continue to dominate the camaign, the two parties facing a consistent downward trend in projections are New Zealand First and Greens.

New Zealand First is now projected to get 9.7 per cent of the party vote and an estimated 11 seats.

For the first time, the Herald model is predicting fewer than 5 per cent of the party vote for the Greens, with the lower and upper estimates showing 4.2 to 5.6 per cent. It's a clear trend with last three all polls showing them at under 7 perent.

The Herald forecast will be updated regularly in the final weeks of the campaign as the results of new polls become available. It'll be more responsive to the polls closer to the election day.