ACT has promised to remove tax on KiwiSaver earnings.

Leader David Seymour unveiled the policy during the party’s campaign launch in Auckland on Sunday.

He said it would allow people's returns to stay invested and generate savings for generations.

"Other parties want to force your money into KiwiSaver, then tax you," he said.

"ACT says it should be your choice, but if you save for the future we will let you get the full benefit of compounding returns instead of taxing you every step of the way."

Seymour said long-term investments benefit from the "magic" of compound interest.

"Interest on interest, year after year, grows your KiwiSaver balance exponentially. 

"Every time you get taxed on your earnings you don't just lose that money, but all the future savings that would be compounded from it."

Seymour used the example of a 20-year-old builder earning $60,000 salary, who would save an extra $209,486 by the time they turned 65 under the policy.

ACT would also end the KiwiSaver government contribution for members who receive employer contributions, and replace it with the new tax relief.

The whole plan would cost about $2.4 billion over four years (including the benefits gained from ending the government contribution).

ACT's fully costed fiscal plan would be released later in the election campaign, its policy document said.

The general election is on November 7.