The Conservatives value marriages where one partner stays at home.
So the Tory tax break would give £150 a year to a married couple with one earner on £35,000 and the other not working, but would not apply to a married couple both earning £15,000 each, unless one stops work or more than halves their income. I have yet to see anybody explain why that is fair, even among those who disagree with JK Rowling's powerful single mother's manifesto and so think a pro-marriage tax break is a good thing in itself.
The Institute of Fiscal Studies had previously set out why fewer than three in ten married couples benefit.
But the IFS' new detailed manifesto analysis of tax and benefits proposals today reveals for the first time how many married couples are excluded from the tax break because husband and wife both work, and earn over £6500.
The answer is that 5.8 million married couples - so 11.6 million people in all - won't get the marriage tax break because they both work and pay tax, and so have no unused personal allowance to transfer.
That is very close to half of all of Britain's married couples who can't qualify because they don't follow the 1950s sole male breadwinner model which the policy rewards. (Another 0.8 million single earner married couples have the wage-earner paying higher rate income tax: they are excluded by the "ProgCon" amendment of excluding higher rate-taxpayers, to avoid a sharply regressive distribution, rather than the underlying "TradCon" policy design that excludes married couples who both go to work).
As today's Institute of Fiscal Studies report sets out:
The only families which can gain from this policy are married couples where only one partner has an income high enough to be paying income tax and the taxpaying spouse is a basic-rate taxpayer.
Out of 12.3 million married couples in the UK, 5.8 million would not benefit because they are both already taxpayers (so there is no unused tax allowance to transfer), 1.6 million would not benefit because neither are taxpayers (meaning that there is no benefit to either partner from a higher personal allowance) and 0.8 million would not benefit because, although only one partner is a taxpayer, they are a higher-rate taxpayer. Four million couples would benefit, a third of all married couples.
David Cameron perhaps rather misleadingly evaded this point by telling Jeremy Paxman on Friday: "No, that's not true ... it depends what they earn". It is rather a technicality to defend a "stay at home" incentive because those who earn less than £5750 could still get £150, when the policy clearly excludes most married women who work.
It also might surprise people just how poorly targetted the tax break is in helping married families with children, though the IFS has also set out why the evidence that marriage causally improves child outcomes is weak:
As the IFS reports:
Even if marriage did improve child outcomes, though, it is not clear that a policy where pensioner families make up more than a third of the beneficiaries and receive 31% of the gains is well targeted. In fact, only 35% of the families who gain from the policy have children, and only 17% have children aged under 5.
Next Left has also pointed out that - despite the symbolically positive and (legally unavoidable) inclusion of civil partners, labour force surveys show they are somewhat less likely to live in the "approved" household structure than other married couples.
So nobody has yet identified a civil partnered couple who do qualify!
That is a further challenge which ought to be put to Tory frontbenchers, in media interviews defending this flagship policy.