A Tory government will introduce a law guaranteeing no rise in income tax rates, VAT or National Insurance before 2020, David Cameron will say.
The Conservative leader will pledge legislation within 100 days of assuming office to ensure rates do not rise in the next Parliament.
But Labour dismissed the pledge as a “desperate last-minute gimmick”.
Party leader Ed Miliband will say later that Tory plans to reduce the welfare budget would mean cuts to tax credits.
He will say the party will put family budgets at risk.
Elsewhere in the election campaign;
- Liberal Democrat leader Nick Clegg will focus on his party’s pledge to offer free schools meals to all children in England
- A decision not to renew the UK’s Trident nuclear submarines could threaten “the survival of our nation”, 20 ex-military officials say in a letter to The Times newspaper
Both the Conservatives and Labour will focus on economic issues with just over a week to go until polling day.
BBC political correspondent Carole Walker said the no tax rise pledge “is intended to convince voters of the Tory commitment” but will also “bind the hands of a future chancellor, even if there was a new economic crisis.”
Mr Cameron will also reaffirm a pledge to raise the tax-free personal allowance to £12,500 over the next five years and increase the 40p tax threshold in line with inflation.
The prime minister will say: “This is the clearest choice on the economy for a generation.
“And beyond the plain facts, it also comes down to gut instinct. When you’re standing in the polling booth, ask yourself: on the things that matter in your life, who do you really trust?
“When it comes to your tax bill: do you trust the people who taxed you to the hilt when they were in power and still haven’t come clean about the taxes they want to increase next time round?
“Or do you trust the Conservatives, who have cut income taxes for 26 million people, and who will cut your taxes again next time?
“We know it’s your money, not government money. You’ve worked for it, you’ve earned it, you should be able to keep it.”
Chris Leslie, Labour’s shadow chief secretary to the treasury, said people would not believe the pledge.
He said: “This is a desperate last minute gimmick from the Tories which nobody will believe a word of. David Cameron broke his promise not to raise VAT last time and if he gets the chance he’ll do the same again.”
Mr Miliband will focus on proposed cuts to the welfare budget, which the Conservatives have said they will reduce by £12bn.
The Labour leader will say analysis from the House of Commons library shows this would mean a £3.8bn cut to tax credits.
Such a cut would cost a family with two children £2,000 in lost tax credits if their incomes hit £29,000, he will say.
Mr Miliband will promise to protect family budgets, ensuring tax credits rise at least in line with inflation.
He will say: “Today I am here to reveal the truth: if the Tories get back in on 8 May your family budget is at risk.
“Another five years of Tory government will mean a plan to double the pace of cuts next year, a plan that puts your family budget, your NHS and our country’s future at risk.
“I ask you this: do you believe what you’ve heard from the Tories in the last five weeks, or what you’ve seen and what your family has felt in the last five years?
“It’s when you remember their record you realise the reality of their plan.”
Nick Clegg, meanwhile, will highlight the Liberal Democrats’ plan to give all primary school children in England free school meals.
The plan, the party says, would benefit 1.9 million youngsters, with parents saving an estimated £400 per child on lunches. It will cost £610m per year.
Mr Clegg said: “Liberal Democrats want every child to have the best possible start in life. That’s why I want every child to have a hot, healthy school lunch.
“We know that giving children a healthy lunch helps them to concentrate in the afternoon and do better in class.”