Key takeaways
- →This is a composite, illustrative scenario for teaching purposes — not a real Treadstone client file.
- →Porting avoids a prepayment penalty by carrying the existing mortgage's rate forward to a new property — but topping up with extra funds for a price gap needs its own, separate rate.
- →A lender blending a port with new funds has to reconcile both the rate and the amortization — it isn't simply the old mortgage plus a second, unrelated one.
- →The ported portion generally can't reset to a fresh maximum amortization just because it's moving to a new property — the combined schedule has to stay within what the file is actually eligible for.
This is an illustrative, composite scenario — not a real client file — built to show what actually happens, mechanically, when a mortgage is ported to a new property alongside a request for additional funds.
Say a borrower is selling their current home and buying a more expensive one, and wants to port their existing mortgage — carrying its low rate and remaining term forward — rather than breaking it and paying a prepayment penalty. The new property costs more, so they also need to borrow additional money to cover the gap. That combination is where the file gets genuinely more complicated than either a straight port or a straight new mortgage would be on its own.
01 · Why did the borrower want to port instead of just breaking the mortgage?
The existing mortgage was locked in at a rate well below what was currently available in the market, with a meaningful prepayment penalty attached if broken early. Porting lets a borrower carry that existing rate and remaining term forward onto a new property, avoiding the penalty entirely — one of the standard tools the Financial Consumer Agency of Canada points to for reducing or avoiding a prepayment penalty.
The complication: the new property cost more than the old one, and the existing mortgage balance alone wasn't enough to cover it. The borrower needed additional funds layered on top of the ported amount.
02 · How did the lender combine the old rate with a rate on the new money?
This is commonly called a “blend and increase”: the lender calculates a new, single blended rate that weights the existing mortgage's rate against the additional funds' current-market rate, based on the proportion of the total mortgage each portion represents.
The exact blending formula is set by each individual lender's own policy — there's no single universal calculation every lender uses — which is exactly why the broker requested a full written breakdown of the blended rate before the borrower committed to the purchase, rather than accepting a single headline number.
See the math before you port
A blended rate is only as good as the breakdown behind it.
Treadstone's fulfillment associates request the full written blend-and-amortization breakdown on every port-plus-funds file, so clients see the real math before committing to a purchase.
03 · What happened to the amortization when the funds were combined?
The ported portion of the mortgage kept the remaining amortization it already had — it doesn't reset to a fresh maximum term simply because the underlying property changed. The new incremental funds needed for the price gap had to be underwritten within whatever overall amortization ceiling the combined file was actually eligible for.
That ceiling matters: a borrower can't simply restart a full 30-year clock on the whole balance unless the file independently qualifies for that (for example, as an insured purchase for a first-time buyer or a new build). The lender combined the two portions into a single reconciled schedule — not by averaging the two amortizations casually, but by working out a combined payment structure that respects the shorter of the two constraints.
04 · What did the broker specifically verify before the borrower signed?
- →A full written breakdown from the lender showing the blended rate calculation, not just the resulting number.
- →Confirmation of the combined amortization schedule, and that it didn't inadvertently exceed what the file was eligible for.
- →A side-by-side comparison of the total interest cost under the blended port versus simply breaking the mortgage and starting fresh, so the borrower could see which was actually cheaper.
- →Written confirmation of the prepayment penalty amount that was being avoided, to make the comparison concrete rather than theoretical.
05 · What's the lesson for other porting-plus-funds files?
“Port plus a top-up” is not addition — it's a reconciliation of two different rates and two different amortization constraints into one new schedule, and the exact method for doing that varies by lender. A borrower shown only the final blended rate, without the underlying math, has no way to judge whether porting was actually the better choice.
Our companion piece on porting vs. breaking a mortgage covers the broader decision; this file is a reminder that even once porting is the right call in principle, the math behind a blended file still needs to be shown, not assumed.
Frequently asked questions
This article is general information to help you scale — not a substitute for tailored advice on your specific business, licensing, or compliance obligations. All figures are illustrative examples for planning purposes; actual costs vary by province, market, and brokerage.