Mortgage Renewal Calculator

What the Mortgage Renewal Calculator does

This calculator answers the question every renewing homeowner actually has: what will my new payment be, and how big a shock is it going to be. It calculates your new payment over your true remaining amortization — not a fresh 25 or 30 years — and shows the dollar and percentage change against what you are paying today.

It goes further than a simple payment comparison. It shows what extending your amortization back out would do to both your monthly payment and your lifetime interest, side by side. It shows what accepting your current lender’s posted offer is likely costing you against a shopped market rate. And it calculates the exact date you should start shopping — 120 days before your term ends, which is when most lenders begin offering rate holds.

• Your new payment, calculated over your actual remaining amortization
• Payment shock in dollars, in percent, and as an annual budget impact
• The balance you will still owe at the end of your new term
• Both sides of an amortization extension: the monthly relief and the extra lifetime interest
• A rate sensitivity table and your ideal start-shopping date

The variables that move the answer — and how lenders treat them

Renewal differs from a first mortgage in one crucial way: the amortization is already partly used up, and that is exactly where borrowers most often get their own numbers wrong.

• Remaining amortization — this is not your original amortization, and using the wrong number is the single most common renewal mistake. If you started with 25 years and are five years in, you renew over 20 years remaining, not a fresh 25. A shorter remaining amortization means a higher payment for the same balance and rate than most people expect.
• New rate versus current rate — the gap between what you were paying and what you are being offered is the entire source of payment shock. Lenders set renewal offers independently of your original rate; nothing requires your renewal rate to relate to your first-term rate at all.
• Lender loyalty — renewing with your current lender usually requires no re-qualification and no new stress test at the same balance and amortization, which is genuinely convenient. But convenience is not the same as the best rate: your lender has no obligation to offer their most competitive number, and posted renewal offers are frequently higher than what the same lender would give a new client.
• Amortization extension — available at renewal in a way it usually is not mid-term. Extending lowers the payment immediately, but every added year extends the period interest accrues over, and the extra lifetime cost is usually larger than borrowers estimate before seeing the number.
• Lump-sum prepayment — renewal is a penalty-free window. You can pay down any amount, over and above your annual prepayment privilege, without the charge that would normally apply mid-term.

How mortgage renewals are actually calculated in Canada

Your new payment uses the same Canadian semi-annual compounding formula as any other fixed mortgage: the periodic rate is derived from your new nominal rate and payment frequency, and the payment is solved against your outstanding balance over your remaining amortization in periods — not reset to a round number of years.

The balance at the end of your new term is calculated by amortizing that new payment forward for the number of periods in the term, which is very often far shorter than the periods left in the amortization. That is why you renew again with a balance still outstanding rather than a paid-off mortgage.

The amortization-extension comparison recalculates the payment over the longer period at the same rate and balance, then compares total interest under both scenarios. The relief and the cost are shown side by side deliberately: a calculator that shows only the lower payment without the interest trade-off is not being straight with the reader.

• New payment: P × i ÷ (1 − (1 + i)^−N), where N is the REMAINING amortization in periods
• Balance at end of term: the new payment amortized through the term length
• Extension scenario: same formula, larger N, same rate — compared on payment and total interest
• Start-shopping date: renewal date minus 120 days, the typical start of a rate hold

How this changes your renewal conversation

A renewal offer letter from your current lender is a starting point, not a final answer. Every number here is designed to be brought into a conversation before you sign anything, because renewal is the one moment in a mortgage’s life when switching lenders costs you nothing in penalties.

• Payment shock — the number to budget for immediately, in dollars and as a share of what you pay now
• Balance at end of term — what you are really renewing again next time, not just what you owe today
• Cost of staying — quantifies what signing a posted offer without shopping is likely costing you
• Rate sensitivity — shows how much a quarter or half point actually moves your payment
• Start-shopping date — the practical trigger to act, well before your rate hold window closes

Using your results well

Start shopping on the date this calculator gives you, not on the day your renewal letter arrives. Lenders typically offer rate holds 90 to 120 days before a term ends, and being ready with your numbers before that window opens is what lets you act on a lower rate rather than just noticing one existed.

What this calculator does not do is guarantee any rate — the shopped-rate figure is illustrative, for comparison, not an offer. It also does not model switching lenders mid-term, which usually triggers a prepayment penalty on your existing mortgage; that is a different calculation entirely.

• Confirm your actual remaining amortization from your lender or statement, not an estimate
• Use the lump-sum field to see what a penalty-free prepayment at renewal would do
• Compare the extension numbers carefully — the lower payment is real, but so is the extra interest
• Talk to a broker before your rate hold window opens, not after you have signed the offer