Pay Down Mortgage vs Invest After Maxing Registered Accounts

01 Why this only starts after the registered accounts are full

The mortgage-vs-invest question only becomes a real toss-up once your RRSP and TFSA are maxed, because those accounts beat both options outright. An RRSP contribution gives an immediate refund at your marginal rate — for Mark at roughly 40%, that's $400 back on every $1,000 — plus tax-sheltered growth. A TFSA grows and comes out entirely tax-free. No mortgage prepay and no taxable account can match a guaranteed 40% headstart or permanently tax-free compounding.

So the honest framing is narrow: you have already filled the registered room, you have surplus cash, and the only remaining homes for it are a mortgage prepay or a non-registered investment account. That is the decision Mark faced, and the rest of this post stays inside it. If you still have RRSP or TFSA room, fill it first — this debate doesn't apply to you yet.

Source: CRA — Tax-Free Savings Account (TFSA) guide

02 The mortgage prepay: a guaranteed, after-tax return

Paying down your mortgage earns a guaranteed return exactly equal to your mortgage interest rate, and in Canada that return is already after tax. Every extra dollar Mark puts against his 5.0% mortgage avoids 5.0% of interest for the remaining life of that balance — money he keeps with certainty, in every market, with no further tax to pay on it.

The "after tax" part is the piece Canadians import wrong from American advice. In the United States, mortgage interest on a primary home is often deductible, which lowers the effective cost of the loan and makes prepaying look weaker. Canada has no such deduction for the mortgage on your own home — interest is only deductible when you borrow to earn investment income, not to buy or hold your residence. So a 5.0% Canadian mortgage costs a clean 5.0%, and prepaying it returns a clean 5.0%. To beat that with investments, you need an after-tax expected return above 5.0% — not a pre-tax one.

The comparison is usually run as a mortgage rate against an expected market return, and stated that way it is not a fair comparison. The mortgage saving is after-tax and certain; the market return is pre-tax and uncertain. Netting the investment for tax before comparing is what closes most of the apparent gap.

Source: FCAC — Paying off your mortgage faster · CRA — Line 22100 carrying charges and interest

03 The taxable investment: a higher number, taxed down

A non-registered investment can expect a higher return than the mortgage rate, but two things shave it down: tax and risk. Start with tax. In a taxable Canadian account, interest is taxed at your full marginal rate; eligible dividends get the dividend tax credit; and only 50% of a realized capital gain is included in income at the current inclusion rate. A diversified portfolio expecting 6.5% before tax does not deliver 6.5% to your net worth — once you account for the drag from tax on distributions and eventually-realized gains, a 40%-bracket investor like Mark nets closer to 5.5%.

Then there is risk. The 6.5% is a long-run average, not a yearly entitlement: the same portfolio can return +20% one year and −15% the next. The mortgage 5.0% is contractual and arrives every single year. Comparing a guaranteed 5.0% to a risky after-tax 5.5% reframes the whole question — you are not choosing between 5% and 6.5%, you are paying a guaranteed return to chase roughly half a point of uncertain extra.

Source: CRA — Capital gains and the inclusion rate

04 Worked example: 5% mortgage vs 6.5% taxable

On Mark's numbers the two paths end up within a few thousand dollars of each other, which is the whole point. Put $12,000 a year for 10 years against a 5.0% mortgage and you save a guaranteed $30,935 in avoided interest. Put the same $12,000 into a taxable account expecting 6.5% before tax — about 5.5% after a realistic 15% effective drag from the 50% inclusion rate and the dividend credit — and you grow about $34,685, an edge of roughly $3,750. That premium is real but thin, and unlike the prepay it is not guaranteed. The calculator opens on his figures; change the rates to your own and watch which pane wins.

On the defaults above, the worked example returns $30,935. Investing wins by $3,751 on after-tax return of 5.5% — but that gain is uncertain, while the prepay is guaranteed.

Source: CRA — How taxable capital gains are calculated

05 Prepay vs invest, factor by factor

Laid side by side across the factors that actually decide it, the two options stop looking like a simple "higher number wins." Read down the column that matches your rate, bracket, and temperament rather than chasing the headline return.

The table exposes the real trade: a prepay hands you certainty and an after-tax rate that is hard to beat, while investing offers a thin expected premium, more risk, and far more liquidity. Liquidity is the one genuine point for investing here — money in a taxable account can be reached in a crisis, while a prepaid mortgage cannot, short of re-borrowing.

Source: CRA — When interest is deductible (carrying charges)

06 The behavioural premium nobody prices in

The spreadsheet edge for investing is real but small, and behaviour usually swamps it.

A guaranteed 5.0% earned every year, with no statement to check and no temptation to sell at the bottom, is worth more to most people than a slightly higher number they have to live through a 30% drawdown to collect. The research on this is unromantic: investors who cannot stomach volatility realize far less than the index returns, because the gap between the investment's return and the investor's return is created entirely by the decisions made during bad years.

There is also the finish line. For Mark at 62, clearing a $180,000 mortgage before he fully stops working drops his required retirement income permanently and removes a renewal-rate risk he otherwise carries to 66. None of that appears in the 5.5%-versus-5.0% comparison, but it is real money and real peace, and it tilts a close call toward prepaying for anyone near retirement.

The honest way to use this is not as a reason to avoid investing, but as a reason to pick the option you will still be following in eight years. A prepayment plan continued through a bad decade beats an investment plan abandoned in year three, and the second is a far more common outcome than the arithmetic suggests. If you know from experience how you behave in a downturn, that knowledge is a legitimate input rather than an excuse.

Source: Amromin, Huang & Sialm (2007) — mortgage prepayment vs tax-deferred saving

07 So which one, and when

Pick by the size of the after-tax gap and your distance from retirement, not by the pre-tax headline. When your after-tax expected return clears your mortgage rate by a wide margin and you have a long horizon and the stomach for volatility, invest — the premium compensates the risk. When the after-tax premium is under about a point, or you are within a few years of retiring, or market swings would change what you do, prepay: you are buying a guaranteed return and a smaller future cost of living for the price of a sliver of uncertain extra.

For Mark the answer was prepay. The after-tax investment edge was only about half a point, his renewal was looming, and he wanted the mortgage gone before he stepped back. He's splitting the surplus 70/30 toward the mortgage while keeping some in the taxable account for liquidity — a perfectly good hybrid. The point is that you choose on the after-tax math, not the brochure return.

Source: FCAC — Paying off your mortgage faster