How does the Mortgage Paydown vs. Borrow-to-Invest Calculator work?
The calculator takes one monthly cash-flow amount and applies it to two different strategies. Strategy A adds the amount to the mortgage payment. Strategy B uses the same monthly amount to estimate an interest-only investment loan, invests the borrowed amount, and later applies the projected net investment equity to the mortgage.
This is designed to answer a practical planning question: “If I can afford an extra $300, $400, $500, $600 or another amount each month, which strategy could potentially help me become mortgage-free sooner?”
The comparison begins with the client’s actual mortgage information: current principal balance, current mortgage interest rate, remaining amortization, payment frequency and regular payment. The calculator then checks whether the stated balance, rate, amortization and payment are reasonably consistent. If they do not reconcile, the tool warns the user instead of quietly producing a polished but unreliable projection.
Strategy A — Put the extra monthly budget directly on the mortgage
The first strategy adds the extra budget to the client’s regular mortgage payment. For example, if the regular payment is $3,500 per month and the household can comfortably allocate another $400, the illustration compares the mortgage using $3,900 per month, subject to the assumptions entered in the calculator.
The result shows the estimated mortgage-free timeline and the estimated interest reduction compared with simply continuing the existing payment. Actual lender prepayment privileges matter, so a client should always confirm how much additional payment or annual lump sum is permitted under the mortgage contract.
Strategy B — Use the same monthly budget to support a borrow-to-invest strategy
The second strategy starts with the same monthly cash-flow budget. Instead of choosing the investment-loan amount first, the calculator works backward and estimates how much interest-only borrowing that monthly amount can service at the applicable investment-loan rate.
The current calculator uses the following illustrative lending spreads supplied for this strategy. The prime-rate input is editable because prime can change:
| Illustrated investment loan | Rate formula | Why it matters |
|---|---|---|
| Under $50,000 | Prime + 1.25% | Higher spread for smaller borrowing |
| $50,000–$99,999.99 | Prime + 1.00% | Middle pricing tier |
| $100,000+ | Prime + 0.75% | Lower spread once the $100,000 tier is reached |
The calculator tests the tiers rather than applying one rate blindly. This matters because a client whose budget is large enough to cross the $100,000 threshold could receive a lower illustrated spread than a client just below that threshold. The rate and loan amount can also be overridden for an advisor illustration.
Worked example: $800,000 mortgage and $400 of extra monthly cash flow
Assume a homeowner has an $800,000 mortgage, is paying approximately $3,500 per month, has about 30 years remaining, and can allocate an extra $400 per month. The calculator lets the homeowner compare adding $400 to the mortgage with using the same $400 to support an investment loan.
Illustrative inputs
- Current mortgage balance: $800,000
- Illustrated fixed mortgage rate: 3.314%
- Remaining amortization: 30 years
- Regular payment: $3,500 per month
- Additional monthly budget: $400
- Illustrated prime input: 4.45%
- Investment period: 10 years
- Illustrated investment return: 7% CAGR
Using Canadian fixed-rate mortgage mathematics, the regular $3,500 payment is approximately consistent with a 30-year payoff under those assumptions. Adding $400 directly to the mortgage reduces the estimated payoff period to roughly 25 years and 2 months.
At an illustrative prime rate of 4.45%, the assumed Prime + 1.00% lending tier allows approximately $88,073 of interest-only investment borrowing for the $400 monthly budget. At a hypothetical 7% annual gross return over 10 years, with an assumed 1% annual investment fee, the investment portfolio would be approximately $156,688 (including around $12,381 of modeled fees deducted over the period). At an illustrative 25% effective tax on the realized capital gain, the estimated gains tax on sale is about $17,154. After repayment of the investment loan and this tax, around $51,461 would remain for the mortgage. Under this set of assumptions, direct mortgage paydown finishes in approximately 25 years and 2 months; borrow-to-invest plus an after-tax lump sum at year 10 finishes in approximately 25 years and 5 months. Thus the direct paydown is about three months sooner in this example. These are model outputs, not expected returns or tax advice; interest deductibility, annual distributions, rate changes, transaction costs and mortgage prepayment penalties are excluded.
These numbers are an illustration, not a promise. A personalized illustration can change the mortgage rate, prime rate, budget, investment period and annual returns to show how sensitive the result is to the assumptions.
Why accurate mortgage math matters
A mortgage-paydown comparison is only useful if the starting mortgage projection is reasonably close to the lender’s amortization calculation. This calculator therefore uses Canadian mortgage conventions rather than a simple “balance divided by payment” estimate.
For a fixed mortgage, the calculator converts the stated annual rate using the Canadian convention of nominal interest compounded semi-annually, not in advance, and then converts that rate to the selected payment frequency. For variable mortgages, the illustration compounds interest at the payment period. The calculation then simulates every payment period until the balance reaches zero.
The tool also calculates the regular payment implied by the entered balance, interest rate and remaining amortization. It compares that payment with the client’s actual entered payment. A close match increases confidence that the statement inputs have been entered correctly. A large difference produces a warning so the user can recheck the mortgage statement.
For the best estimate, use the current principal balance as of today, the current mortgage rate, the actual payment frequency, the current regular principal-and-interest payment, and the remaining amortization shown by the lender. Property taxes, home insurance and unrelated fees should not be included in the mortgage payment field.
Flat return or year-by-year returns: which is more useful?
A flat return is useful for a quick illustration, but real investment returns do not arrive in a perfectly straight line. The year-by-year mode lets users model positive years, negative years and mixed market periods while still seeing the actual compounded annual growth rate.
The calculator provides two investment-return methods:
- Flat Annual Return: enter any annual assumption, such as 6%, 8%, 12%, 15% or a custom figure.
- Year-by-Year Returns: enter a different return for every year of the selected investment period.
Year-by-year mode includes preset paths for Realistic Mix, Early Downturn, Mid Downturn and Late Downturn. Every annual box remains editable. The calculator shows both the arithmetic average and the actual compounded annual growth rate (CAGR).
One mathematical point is worth understanding. In this particular calculator, the investment is one lump sum at the beginning and there are no additional investment deposits or withdrawals during the selected investment period. Therefore, simply changing the order of the exact same annual returns does not change the ending portfolio value. It changes the path experienced along the way. If the annual return values themselves change, the final value changes.
What does “net investment equity” mean?
Net investment equity is the projected investment value, after estimated ongoing investment fees, minus the outstanding investment-loan principal and estimated capital-gains tax on sale. The calculator also shows the pre-tax equity and any loan-repayment shortfall.
For example, if a $100,000 investment loan grew to a projected account value of $200,000, the calculator would not show $200,000 as available to pay down the mortgage. It would first subtract the $100,000 investment loan, leaving $100,000 before realized capital-gains tax and other selling costs. The actual amount available for the mortgage will generally be lower when tax is payable.
This keeps the comparison fair. Otherwise, the leveraged strategy would appear artificially stronger because the borrowed principal would be counted as if it belonged to the client free and clear.
What happens when prime or the mortgage rate changes?
Both rates can materially affect the comparison. A prime-based investment loan can become more or less expensive when prime changes. A mortgage may also renew at a different interest rate before the projected payoff date.
For that reason, the prime-rate field is editable and the calculator does not permanently hard-code a borrowing rate. The mortgage rate is also an input. The current projection assumes the entered mortgage rate remains constant for the illustration unless the user changes it. A future version could model multiple mortgage renewal periods, but a single-rate assumption keeps the client-facing calculation understandable and transparent.
Who may find this comparison useful?
This calculator may be useful for homeowners who have positive monthly cash flow, a long investment horizon and an interest in comparing debt reduction with a leveraged investing strategy. It can also help couples understand that the real decision is not necessarily “mortgage or investing” in the abstract. The practical question may be how to deploy a fixed monthly amount that already fits within the household budget.
Borrowing to invest increases both opportunity and risk. Investment values can decline, prime can rise, and the mortgage still needs to be serviced. A strong illustration should therefore be tested at several return assumptions and not only at the most optimistic scenario. That is why the calculator includes conservative flat rates and editable year-by-year returns.
How an illustration supports a better client discussion
- Start from the current mortgage statement information, entered as accurately as possible.
- Use the extra monthly amount the household can comfortably allocate without relying on future investment gains.
- Confirm the current prime-rate input and the applicable investment-loan spread.
- Run a conservative return assumption first.
- Then test higher and lower returns, including at least one negative year.
- Compare the mortgage-free timeline, not only the investment account value.
- Review mortgage prepayment privileges and any potential penalties before assuming a future lump-sum payment can be made without cost.
- Keep the PDF, or receive the result by email, WhatsApp or text for later discussion.
Frequently asked questions
Is it better to pay extra on a mortgage or invest in Canada?
It depends on the mortgage rate, investment return, risk tolerance, time horizon, taxes, fees and whether borrowing is involved. Extra mortgage payments provide a predictable reduction in debt and interest. Investing may create a higher long-term value, but the outcome is uncertain. This calculator compares both approaches using the same monthly cash-flow budget.
How much sooner can I pay off my mortgage by adding $400 per month?
The answer depends on the current mortgage balance, interest rate, payment frequency, regular payment and remaining amortization. With those figures and an extra monthly budget of $400, the illustration simulates the remaining payments and shows the estimated time saved.
How much can $400 per month support for a borrow-to-invest loan?
The amount depends on the applicable investment-loan interest rate. For example, using a 4.45% prime rate and a Prime + 1.00% spread, a $400 monthly interest budget supports approximately $88,000 of interest-only borrowing. Ask Pankaj Bhatia for an updated illustration with a different prime rate or monthly budget.
Why does the borrowing rate change at $50,000 and $100,000?
The calculator uses tiered spread assumptions. Under the current illustration, loans below $50,000 use Prime + 1.25%, loans from $50,000 to $99,999.99 use Prime + 1.00%, and loans of $100,000 or more use Prime + 0.75%. Always verify the lender’s current pricing and qualification rules.
Can I enter a 12-year or 15-year investment period?
Yes. An illustration can use a preset period or any custom period, and the year-by-year mode creates the corresponding number of annual return boxes.
Can I enter a 16% or another custom rate of return?
Yes. An illustration can use any flat return assumption or a separate return for every year. Higher return assumptions can materially change the result and should be treated as illustrations rather than expected or guaranteed outcomes.
Does the calculator use gross investment value to pay off the mortgage?
No. It first subtracts the original investment-loan principal from the projected investment value. Only the remaining projected net investment equity is applied against the mortgage in the illustration.
What happens if the investment loses money?
The year-by-year return mode accepts negative returns. If the investment value is below the investment-loan balance at the selected horizon, the calculator does not pretend there is positive equity available for the mortgage. This helps test less favourable scenarios before making a decision.
Does the calculator include tax deductions on investment-loan interest?
No. The base comparison intentionally excludes tax benefits because deductibility depends on how borrowed funds are used and the taxpayer’s circumstances. Tax rules and documentation requirements should be reviewed with a qualified tax professional.
Can I share the illustration with a client or spouse?
Yes. Pankaj Bhatia can provide a client PDF, an email, WhatsApp or text summary, or a private link that opens your illustration for a limited time. The shared content reflects the actual calculation results.
Calculation methodology and sources
The mortgage calculation engine is designed around Canadian mortgage conventions and is intended to produce a close educational estimate when accurate statement inputs are used. It is not a replacement for a lender payout statement or mortgage-administration system.
- RBC Royal Bank mortgage rates and mortgage information — reference for Canadian mortgage-rate conventions and lender information.
- RBC Royal Bank Prime Rate — reference for the prime-rate input used in the investment-loan illustration.
- CMHC Mortgage Calculator — public Canadian mortgage-calculation reference using mortgage amount, interest rate, amortization and payment frequency.
Last reviewed: October 7, 2026. Prime rates, lender pricing, tax rules and product terms can change. The current inputs should always be verified before presenting an illustration.