The Conservatives say they can cut £4bn in taxes, increase public spending and have sound finances.
"By going to war on waste and ending ineffective public spending programmes", they say, they can lower taxes, reduce borrowing and raise overall spending by 4% a year - compared with 5% under Labour.
The claim sparked derision from Labour, with Tony Blair dismissing it as "economic nonsense".
TORY SPENDING PLANS: THE FACTS
At this stage it is not possible to say definitively who is right. Here is BBC political editor Andrew Marr's verdict on the claim and counter-claim:
The prime minister accuses the Conservative leader of manifesto fraud - a wild three-card trick of higher spending, tax cuts and sound finances. And in return, Michael Howard accuses Tony Blair of lies.
In truth, the Tories could save a bit but establishing the final truth about spending pledges is horrendously difficult.
Take today's example: Michael Howard ridiculed Labour for costing his promised drug rehabilitation scheme at £1.2bn. It cost less than half of that, he said.
So, where had Labour got the figures from? Answer, a Tory website. A little embarrassed, the Conservatives responded that there were now newer, better figures which showed drug rehab costs were less.
This was a small spat perhaps, but it goes to the heart of one of the problems in an election: producing detailed costings about the future is very hard.
How much would extra prison places cost? Well, that depends where the prison is built, to what specifications, cost overruns and the rest.
We must beware bogus precision. Establishing truth in detail is often like nailing jellyfish to a wall - painful, cruel and ultimately pointless.
WHAT THE THREE MAIN PARTIES SAY
Labour has accused the Tories of publishing a "fraudulent prospectus" with spending commitments they could not afford.
Arguing it was impossible to cut taxes, raise spending and borrow less simultaneously, Tony Blair said: "It's economic nonsense."
The Liberal Democrats say the Tory sums do not add up. Only £13.3bn of their £35bn planned efficiency savings are new, they say, and £8.2bn of them are "unachievable".
But the Tories say their plans are costed for the entire Parliament and are backed by the independent Institute for Fiscal Studies.