Well-heeled Canadians have hidden up to $240.5 billion in foreign accounts and are dodging up to $3 billion a year in federal tax on those funds, according to the CRA's first ever attempt to estimate how much government revenue is lost from individuals stashing money abroad.

The Canada Revenue Agency arrived at the figure as part of its effort to calculate the country's "tax gap" — the difference between how much the government would collect if everyone paid what they owe, and how much the government actually takes in.

"Imagine if that money was coming into productive investments in Canada building our economy," said Diana Gibson of the advocacy group Canadians for Tax Fairness. "Imagine how many jobs you could get off of that."

The figures released Thursday show that there's another $429 billion held abroad that law-abiding Canadians have declared, largely in the form of property, stocks and bonds. Most of that above-board wealth is invested in the U.S. or China, the CRA report says.

Squirrelling money in foreign locales to dodge tax became a hot-button issue in recent years in the wake of the Panama Papers and Paradise Papers leaks, which blew the lid on billions of dollars in worldwide tax evasion and other financial crimes taking place via the shady milieu of offshore havens.

Rough estimates by other organizations of how much money the Canadian treasury loses as a result of those hidden accounts have ranged up to $20 billion annually, but the CRA had never previously produced an official number, for which it faced criticism. A dozen other Western countries calculate their tax gaps.

P.E.I. Senator Percy Downe is among those who had criticized the CRA for not estimating Canada's tax gap. (Steve Bruce/CBC)

Much more hidden wealth possible

The CRA claims it's getting better at ferreting out tax cheats who don't declare their foreign assets, with an additional $284 million in unpaid taxes discovered in the last three years and 1,100 audits underway. Just this year, about 100 countries, including Canada, have begun sharing information on foreigners who have bank and investment accounts within their borders.

The agency's new estimates released Thursday are rough figures only, based on crude calculations of the total amount of hidden stocks, bonds and bank accounts owned globally. That aggregate is thought to be between $6.3 trillion and $9.1 trillion as of 2013, the CRA report says, citing various academic studies.

Canadians account for anywhere from 1.2 per cent to 2.6 per cent of that wealth, the CRA says. That translates to between $75.9 billion and $240.5 billion in hidden assets, as of 2013, representing potential federal tax revenues of between $800 million and $3 billion in 2014.

"It's sort of on the low end of what we expected," said Gibson of Canadians for Tax Fairness. "We've done some number crunching that would put this at $5 billion to $7 billion" in lost tax, she said.

There could be much more hidden money and unpaid tax to be discovered, as the CRA has yet to estimate the tax gap for domestic and foreign holdings of corporations.

The CRA's latest numbers also don't only account for money hidden in tax havens, because the agency uses a very liberal interpretation of "offshore" wealth that includes any jurisdiction outside Canada.

Deficit could be wiped out

Overall, including domestic and foreign tax dodging, Canada's tax gap is now estimated to be at least as much as $14.6 billion a year based on 2014 data, the CRA says — the equivalent of 5.3 per cent of all federal revenues. That's enough money to plug the entire projected federal government deficit for next year.

The total tax gap that the CRA has calculated so far comes from:

The up to $3 billion in unpaid personal income tax from foreign holdings.

$8.7 billion in unpaid personal income tax from domestic income, which the CRA calculated last year.

$2.9 billion in unpaid GST, reported on in 2016.

Denis Meunier, a former director general of enforcement at the CRA, said it's crucial the government have these kinds of tax-gap numbers so it can assess whether its collection efforts and tax-related policies are having an impact.

"It's important that we know these figures, and it's more important to know the changes over time. If you repeat the same methodology, if they do this every few years, you can determine if the gap is growing relative to GDP," Meunier said.

"And that should give you an appreciation, both the public and the CRA, of the work that it is doing and whether it's making a difference."

The parliamentary budget officer is also planning to publish its own study of Canada's tax gap and had been fighting the CRA for years to get relevant data. That study could come as early as this fall.