The Green Party's plan to bring in a national pharmacare plan would cost close to $27 billion in its first full year, according to the national budget watchdog.

Green Party Leader Elizabeth May released the Parliamentary Budget Office's costing of 24 planks of her party's platform this morning during a stop in Halifax. The PBO also posted its findings online.

The spine of the platform is a commitment to a 60 per cent cut in emissions below 2005 levels by 2030, doubling the current 30 per cent target. Other marquee promises include bringing in a universal drug plan and abolishing tuition fees.

Pharmacare is the most expensive line item in the Green Party's platform, with a price tag steadily increasing to $31 billion in 2024-2025. The next costliest item in the platform is the free tuition promise, which would cost $16 billion in 2020-2021.

May said some of the initiatives would be financed by boosting the federal corporate tax rate to 21 per cent from the current 15 per cent — which the PBO estimates would bring in close to $13 billion next year.

The Greens are also promising to impose a financial transactions tax of 0.5 per cent to collect nearly $18 billion in 2024-2025 — higher than the 0.2 per cent increase they mentioned in the platform last week.

The platform also includes a new tax on sugary drinks, which the PBO said could bring in more than $300 million annually.

The Greens promise to balance the budget by 2024-2025, though May said her government would respond to economic circumstances.

The Liberals and NDP have also talked about pharmacare on the campaign trail.

Yesterday, Liberal Leader Justin Trudeau said a Liberal government would spend $6 billion as a "down payment" on implementing pharmacare, but offered few other details.

The NDP is promising to bring in a universal pharmacare program within one year if elected. The party's costing is based on the PBO's 2017 conclusion that a national plan would cost nearly $23 billion to implement in 2020.

The NDP plan also depends on negotiations with the provinces and territories.

"Our plan to build a pharmacare program would require a $10 billion investment from the federal government and then it would use the resources that are already being spent in each province, so each province already has a pharmacare program, and so we would ask to pool our resources together," Singh told reporters on Wednesday.

Politics of PBO costing

This is the first federal election campaign since the Parliamentary Budget Office received a mandate to cost out election promises.

The goal behind the costing analysis is to give political parties more certainty and enhanced credibility, although parties aren't obligated to use the independent office's services.

The PBO has costed 12 Conservative plans and three of the NDP's promises, so far.

The tool has become a political issue during this campaign already, with the Conservatives accusing the Liberals of trying to hide the costs of their campaign promises.

A Liberal spokesperson said the party is working with the PBO on the costing of specific electoral proposals.

The Conservatives have promised to use the PBO to cost "every platform commitment that has dollars and cents attached to it," said party spokesperson Simon Jefferies.