The party will enter the race with a pledge to cut taxes and take low earners out of income tax entirely.
Leader Nigel Farage said its policies would ensure that people "get out and spend" and "actually help to get the economy going".
UKIP would also make the 40p rate the top rate of tax, which people would start to pay once they earned £45,000.
Mr Farage confirmed last month that the party was rethinking its economic policies and that it no longer backed a single rate of income tax.
In 2010, when he was not leader, it supported a "flat tax", which it said would be set at 31% and would be achieved by merging income tax and national insurance.
'Worthwhile'
But Mr Farage last month said he believed an appropriate top rate of tax was 40%. He also announced that no-one earning the minimum wage or below should pay any tax on their earnings.
Mr Farage told the BBC News Channel: "The most important thing is raising the threshold at which people start to pay tax."
He added: "If you do that whilst at the same time controlling the over-supply of labour that's coming into Britain from many parts of Europe, not only do you get people back into work, you make it worthwhile for people to get off benefits."
Mr Farage said full details of how UKIP would pay for the tax changes would be outlined at the party's annual conference next month.
He added: "When you leave people more money in their pocket they actually go out and spend it in the economy. That actually helps to get the economy moving."
The party would also block new migrants from claiming benefits until they had paid tax and national insurance for five years. BBC.
