The National Party has won its appeal over how much it must pay for breaching the copyright of Eminem's Lose Yourself in a 2014 election ad.

In a decision released today, the Court of Appeal allowed the National Party's appeal - and reduced the damages payment down from $600,000 to $225,000.

"On the evidence, the proposition the National Party turned a blind eye to the risk of copyright infringement or saw a risk and embarked on a reckless course of conduct with respect to that risk was not sustainable," today's decision says.

The National Party had used the track 'Eminem Esque' in a 2014 TV campaign advertisement.

The High Court later ruled the similarities between Lose Yourself and Eminem Esque were so strong it breached copyright.

In July the National Party went to the Court of Appeal to fight a ruling that it must pay for breaching copyright in a 2014 election ad, which played a song similar to Eminem's Lose Yourself.

Lawyers for the party argued the total damages of about $600,000 ordered by the High Court last year were too high, and that the judge took a "licensor-centric" approach.

The then-Government fought its case in May last year, accused of knowingly trying to sidestep licensing fees by using the track Eminem Esque.

The High Court ruled the similarities between Lose Yourself and Eminem Esque were so strong and it breached copyright.

It noted publisher Eight Mile Style had exclusive control of the song's licensing, and rarely granted permission for the song to be used in ads.

Justice Helen Cull said the $600,000 would be the "hypothetical licence fee" that would have reasonably been charged for permission to use Lose Yourself in National Party advertising, including interest from June 2014.

In court this morning, lawyer Greg Arthur said an expert the judge relied on when setting a figure for damages had no relevant New Zealand experience, and her base fee was a "significant percentage higher" than it should have been.

He said a number of factors should have been taken into account when the figure was set, including the fact the National Party had alternative pieces of music it could have used instead of Eminem Esque.

The object for the party was to find a "syncopated beat" that matched the row strokes of the rowers in the video, not to copy Lose Yourself.

Given the music would only be used in New Zealand for 11 days, the party would not have gone to the top of the price range for music.