Is it the same percentage of people who will be dead when CPP dries up due to our low birth rates?
Except, this isn't on pace to happen. CPP is fully funded for the next 75 years.
The need is to maintain the same ratio of working age population to retirees. By upping CPP contribution rates substantially more than 2 decades ago, we resolved this issue, fully.
Now, as life expectancy grows, we will have an issue, eventually, and if the birth rate fell further absent some reasonable level of immigration in the working age demographic, we would have a problem once more.
But based on a much lower level of immigration than we have today, CPP is stable.
There is a somewhat larger issue with OAS/GIS in that these are funded cash-from-current each year by Parliament, as opposed to being deducted from pay cheques.
However, even there, the levels of population growth from immigration (and natural growth, for now), is sufficient for fiscal health.
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I would argue for raising the retirement age to 70, and has been done through much of Scandinavia, but largely using the proceeds from that to increase benefits.
ie. CPP delayed to 70 pays 40% more than CPP paid starting at 65. (that is the actual math, I had it done for me by the Parliamentary Library through my MPs office)
So you could go from 33% income replacement via CPP to 46.5% by delaying the age of eligibility.
OAS currently pays 13% of income on average, so a similar bump to ~18.5% for grand total of 58.5% without GIS.
GIS is a bit more complicated, because the former two moves would make most people ineligible, so you would have to raise the income threshold for qualification and the maximum payment, but roughly, we should be able to guarantee someone in the range of 60% income replacement or $2,200 per month, whichever is higher. Which would be a significant lift for many low-income seniors........... But I digress.
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I'm certainly not anti-immigration, but I am for looking at the total allotment of persons entering Canada to live through the Immigration, TFW and Foreign student streams, and moderating that to a level that allows us to catch up on housing and infrastructure, which would probably be about a 20-25% cut from the current target numbers; perhaps a bit deeper for just a year or two.