MacKay's decision, announced last week, means he will be able to collect his full yearly pension of $128,832 at age 55, instead of 65.
Under new pension rules for MPs passed in 2013, all politicians elected after the next election must wait until age 65 before they can draw a pension.
In MacKay's case, those 10 years represent almost $1.3 million.
His current salary as an MP — $167,400 — combined with his $80,100 top-up as a cabinet minister totals $247,500 annually.
MacKay was first elected to Ottawa in 1997 as MP for Pictou County and has been a cabinet minister since 2006. He told reporters in Stellarton last week that he's not reoffering in the next election so he can spend more time with his wife Nazanin Afshin-Jam, their son Kian and their second child, due in the fall.
MacKay is the latest in a list of more than 30 Conservative MPs who have said they are not planning to reoffer. That includes a handful of sitting or former cabinet ministers under age 50, including John Baird, Shelley Glover and Christian Paradis.
A spokeswoman from MacKay's office refused to comment Monday on whether the upcoming change in pension rules played a role in the timing of his departure.
"He is not reoffering so he can spend more time with his family," she said.
Contributions will triple
The Canadian Taxpayers Federation fought for the new rules for MP pensions, which it criticized for being "too generous." The federation has said the new rules should bring them more in line with other plans.
MPs elected in 2015 will be expected to triple their annual pension contributions — from $11,000 a year currently to $39,000 by 2017. It's a change that will bring federal politicians closer to a split with taxpayers, who have been paying most of the shot.
Taxpayers contributed almost $30 million to the federal plan in 2011-2012.
"For every $1 paid in by members of Parliament, almost $24 was being put in by the taxpayer," said Aaron Wudrick, the federal director for the Canadian Taxpayers Federation.
"We think that is really out of whack with what most Canadians can expect from their pensions. The new rules will see that ratio brought down to about $1.62 per dollar — so not quite one-for-one, but certainly a lot more reasonable in terms of what taxpayers are expected to contribute."
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