This will be a big Budget.
Big tax rises, big borrowing, big spending.
And big politically – because it will set the political landscape for the years to come.
Chancellor Rachel Reeves will promise that she will “invest, invest, invest” and will tell the Commons: "My belief in Britain burns brighter than ever.
"More pounds in people’s pockets. An NHS that is there when you need it.
"An economy that is growing, creating wealth and opportunity for all."
Note the upbeat tone, after no shortage of the bleak from ministers recently.
The government is also emphasising that it is “protecting working people’s payslips” – which is code for National Insurance paid by employers, rather than employees, going up – one of the biggest rows of the last few weeks.
Expect Labour to try to use this Budget to attempt to open up a political dividing line with the Conservatives – rather similar to the one Gordon Brown tried a decade and a half ago - where they advocate what they call “investment”, ie spending, and contrast that with what they will label the “decline” offered by the Tories.
Conservative leader Rishi Sunak – on his last big day in the job before his successor is elected on Saturday – will, unsurprisingly, strongly criticise the Chancellor later.
"She’s called National Insurance a 'jobs tax' which 'takes money out of people’s pockets'," he says.
"And worst of all, she said the problem with National Insurance 'is that it is a tax purely on people who go to work and those who employ them'.
"Far from protecting working people she would be raising literally the only major tax that specifically hits working people."
It is expected the Liberal Democrats will focus on social care and the availability of GP and dentist appointments in their response to the Budget.
It is 14 years and seven months since a Labour Chancellor waved the Budget Red Box on the step of 11 Downing Street.
Wednesday 24 March 2010 was the day of Alistair Darling’s third Budget, delivered on the eve of an election campaign Labour would go on to lose.
Incidentally, what was the most expensive measure that day? A promise, costing £600m, to increase the Winter Fuel Allowance for another year.
A Labour idea that would continue throughout the coalition and Conservative years of power, only to be cancelled for the vast majority of pensioners when Labour won again back in July.
For 800 years, men have run the nation’s finances. There have been 110 Chancellors since Sir Richard Sackville was appointed in 1559 - a centuries’ long unbroken line of blokes - which includes Henry Bilson Legge (three times chancellor in the 18th century), and William Gladstone, who had four goes at it in the 19th century.
Until, that is, the appointment of Rachel Reeves.
The Conservatives may have managed the first three female prime ministers, with Labour’s record currently zero, but the first Budget from a female Chancellor of the Exchequer is a genuine moment of history.
So, what can we expect?
Well, the big stuff has been talked up in advance – through nods and winks, official briefings and unauthorised leaks.
There are tax rises, expected to include employer National Insurance and inheritance tax.
There is the change in the government’s self-imposed debt rules, so it can borrow a lot more.
There is the rise in the minimum wage.
There is money to rebuild schools in England.
And the plans for new equipment for the NHS, such as scanners and radiotherapy machines.
Expect a lot of talk from Rachel Reeves about what she will call “choices".
Her team see it as a “once in a generation” Budget, where its scale, it is claimed, matches the scale of the challenge they face.
Which is code for the country’s in a mess and they think it’s going to cost a lot to fix it.
The extent to which it is - and whether billions of pounds more of taxpayers’ money are the solution - are the open questions.