''I am a convert. That's why I have a convert's zeal on this,'' he said.

His policy grants working mothers six months' leave on full pay, capped at a salary of $150,000. If the father is the baby's primary carer, he will receive the payment at the mother's salary. The scheme also applies to same-sex couples.

The net cost will be $6.1 billion and about half of that will come from the 1.5 per cent levy on taxable incomes over $5 million of the 3000 largest Australian companies. This will be offset by a cut in company tax, from 30¢ in the dollar to 28.5¢.

The rest of the money will come from ''associated reductions in other outlays'', according to the Coalition's policy document. This is understood to include income tax receipts on the leave payments, savings on family tax benefit payments and not having public servants ''double-dip'' with state-based parental leave schemes.

Mr Abbott said the business levy would not be permanent but he would not commit to an end date for it. Unlike the government's more modest scheme - which offers 18 weeks' pay at the minimum wage - superannuation will be paid during the Coalition's maternity leave plan.