Lowest Mortgage Payment vs Lowest Total Cost

Direct answer: The lowest mortgage payment is not always the lowest-cost renewal offer. A lower payment can come from a longer amortization, slower principal repayment or different term structure. Compare total term interest, net switching cost and ending balance before treating a low payment as savings.

Use the Mortgage Renewal Offer Analyzer Canada to compare payment and total term cost side by side. You can also ask the usecos mortgage renewal GPT to collect the inputs and call the same API. See the validation methodology for calculation checks.

Why payment and cost differ

Measure	What it tells you	What it can hide
Scheduled payment	Monthly cash-flow pressure	Slower repayment and higher ending balance
Interest during term	Borrowing cost during the contract	Fees and cashback outside interest
Principal repaid	Debt reduction during the term	Monthly affordability stress
Ending balance	Debt left at the next renewal	Future rate uncertainty
Total term cost	Interest plus net switching cost	Non-financial contract features

Worked example

Assume a $425,000 balance, five-year term, monthly payments and semi-annual compounding. The lower-payment offer extends the amortization to 25 years at 5.09%. The lower-cost offer uses an 18-year amortization at 4.79%.

Result	Lower payment offer	Lower total-cost offer
New amortization	25 years	18 years
Scheduled payment	$2,493.64 monthly	$2,929.22 monthly
Interest during term	$101,305.27	$91,338.31
Principal repaid	$48,313.17	$84,414.61
Ending balance	$376,686.83	$340,585.39
Total term cost	$101,305.27	$91,338.31

The lower-payment offer saves $435.58 per month, but it costs $9,966.96 more during the term and leaves $36,101.44 more debt at the next renewal.

When a lower payment may still be reasonable

• Cash flow is temporarily tight and the borrower understands the higher future balance.
• The lower payment avoids higher-cost debt elsewhere.
• The borrower plans extra payments later and the mortgage contract allows them.
• The alternative higher payment would be unaffordable under a realistic household budget.

Methodology and limitations

The example uses the usecos renewal engine, a shared $425,000 balance, monthly payments, Canadian semi-annual compounding and no switching costs. It compares term cost, not lifetime cost after future renewals. It excludes income shocks, optional insurance, prepayment restrictions, variable-rate movement, lender approval and suitability advice. Verified July 30, 2026.

Sources: FCAC mortgage terms and amortization; FCAC choosing a mortgage; FCAC interest on mortgages; Interest Act, section 6.