A ported mortgage that came up short on closing day math

The situation

Ten days. That was what stood between the family and losing their lender's portability window entirely, and it was the number Budi kept repeating on the phone when he first called our office, as though saying it again would make it feel less urgent. Budi had bought a small home in Brampton a few years earlier and still had a mortgage on it, one with a rate he had locked in when rates were noticeably lower than current offerings. When his sister Ishara and her husband Dilshan arrived in Canada, the plan was for all three to combine their savings, sell Budi's home, and buy a larger one together so the newcomer couple would not need to rent while they got established and rebuilt their finances from scratch.

Dilshan worked as a grocery clerk and Ishara as a hairdresser, both newer jobs since arriving and both still on probationary pay scales, and between the three incomes and Budi's existing equity they had put together enough for a home in the $280,000 to $450,000 range. Budi's lender agreed in principle to let him port his existing mortgage to the new property, keeping his current interest rate rather than losing it to whatever new-rate mortgage was on offer that week. Portability sounds simple in theory: the old mortgage moves with you to the new home, rate and all. In practice it only covers the balance still owing on the old loan, and the new home, being larger and meant to house three adults instead of one, cost meaningfully more than the old one had.

The gap between what the ported mortgage covered and the new purchase price needed to be filled somehow, and the lender's solution was a blended rate: a mix of Budi's old, lower rate on the ported portion and a new, higher rate on the additional amount borrowed. The lender sent over a blended rate offer with a deadline attached, tied to the same portability window that was about to close, presented as a take-it-or-lose-it package rather than a starting point for discussion. Budi, worried about losing the deal entirely and unfamiliar with how much room there usually is to push back on a lender's first number, wanted to sign whatever the lender sent and move on with the closing.

That was the state of things when he called us: a signed agreement of purchase and sale, a closing date fixed, a family eager to stop living out of suitcases in a one-bedroom rental while they waited, and a mortgage offer none of them had time, or fully felt equipped, to evaluate properly on their own.

The complication

The complication was not that porting had gone wrong. It was that porting was working exactly as it was supposed to, and the family had assumed that meant the terms attached to it were automatically fair. A blended rate calculation is a formula, weighting the old rate against the new rate by the proportion of each amount in the total mortgage, and lenders do not always calculate it the same way or offer the same spread on the new-money portion.

When we reviewed the numbers the lender had sent, the blended rate they proposed weighted the new-money portion more heavily than the ported portion actually justified, and the rate offered on that new money was noticeably higher than what a competing lender was quoting newcomer clients with comparable income at the time. On a mortgage in this range, even a modest difference in the new-money rate compounds into thousands of dollars over a five-year term. Budi's instinct, understandably, was to avoid rocking the boat with ten days on the clock. He told us more than once that he just wanted the fastest, cheapest way through, meaning the least amount of paperwork and the least amount of our time, even if that meant accepting the first number.

That instinct was the real risk in the file. A rushed signature on a blended rate offer is difficult to undo once the mortgage funds and the deal closes; renegotiating after the fact usually means refinancing, with new legal and lender fees on top of whatever was lost to the higher rate in the meantime. The math favoured spending a few days pushing back now, even against a ticking deadline, over living with an unfavourable rate for years. Convincing Budi of that, while the calendar kept moving, took as much of the file as the mortgage review itself.

There was a second layer, too. Because Dilshan and Ishara were newer to Canada and did not yet have an established credit history here, the family had less room to simply walk to a different lender and start over from scratch if the port fell through. Working within the existing lender relationship, rather than against it, was the more realistic path.

What we did

1. Reviewed the lender's blended rate worksheet against the actual outstanding balance on Budi's original mortgage and the purchase price of the new home, because the family had no way to independently check whether the lender's math was applying the port correctly, and worksheets like this are rarely explained line by line to the borrower. Rebuilding the calculation from the underlying balances, rather than accepting the lender's summary figure, was the only way to know whether the offer was actually fair before anyone signed anything.
2. Identified the specific error in how the new-money portion had been weighted, and flagged that the rate offered on that portion was out of line with what was available elsewhere for comparable borrowers, giving the family something concrete and specific to raise rather than a vague complaint about feeling like the numbers seemed high. A precise, sourced discrepancy is far harder for a lender to wave away than a general sense that the deal feels expensive.
3. Talked through the real cost of rushing with Budi directly, laying out in dollar terms, over one year and over the full term, what accepting the first offer would mean compared to the modest delay involved in pushing back, since his instinct to avoid conflict with the lender was working directly against the family's own financial interest. Seeing the five-year figure in writing, rather than hearing it described in the abstract, was what actually changed his mind about waiting a few extra days.
4. Contacted the lender's mortgage specialist in writing, before the portability deadline expired, requesting a corrected blended rate calculation and referencing the specific discrepancy in the weighting directly rather than asking generally for a better deal, which tends to get a generic response. Putting the request in writing, tied to the deadline still on the file, also created a clear record of when the correction had been raised, in case the timeline became an issue later.
5. Negotiated a short extension to the portability window with the lender, buying a few additional days so the family was not forced to accept a rushed answer under the original deadline while the correction was still being reviewed internally by the lender. Without that extension, the family would have faced a choice between signing the flawed offer or losing portability altogether, which is exactly the pressure a hard deadline is designed to create.
6. Reviewed the revised offer the lender sent back line by line, confirming the new-money rate had been brought closer to market and that the blend was calculated correctly this time, before advising the family it was reasonable to sign and that further pushing was unlikely to move the number further. That final check mattered as much as the original review, since a corrected worksheet still needed to be verified rather than simply trusted because it looked better than the first one.
7. Completed the standard closing work on the purchase itself, including title review, the standard closing adjustments and the mortgage instructions, coordinating so the corrected mortgage terms and the purchase closing landed on the same day without a further gap or a second scramble against the calendar. Lining these up together meant the family's moving plans, already delayed once by the negotiation, did not slip a second time over routine paperwork.
8. Walked the family through the final mortgage documents in plain language before signing, confirming Dilshan and Ishara, as new signatories on the loan alongside Budi, understood the blended rate structure and their joint obligations under it, since all three names would appear on the mortgage going forward. Making sure all three understood what they were signing, not just Budi as the original borrower, mattered because all three would carry the payment obligation equally from closing day forward.

The outcome

The lender agreed to the corrected blended rate calculation, bringing the new-money portion down to a level in line with comparable offers, and extended the portability window by just enough to accommodate the correction without endangering the closing date the family had already planned their move around. The family closed on schedule, into the home they had planned for, with a mortgage that reflected Budi's original rate properly protected on the ported portion and a new-money rate that matched what other lenders were actually quoting.

The difference was not dramatic on paper, a percentage point or so on part of the loan, but over a five-year term on a mortgage in the low hundreds of thousands, it worked out to real savings, likely in the thousands of dollars once compounded across the term. More importantly for the family, it meant the ported mortgage did what portability is supposed to do: protect the benefit of a good existing rate, rather than let a rushed blended calculation quietly erode most of that benefit before the family even moved in.

Budi has since told us he was ready to sign the original offer the day it arrived, and that the few extra days of back-and-forth felt uncomfortable at the time, like he was risking the whole purchase over what felt like a small point. Dilshan and Ishara, settling into steadier work since the move and now a year into building credit history of their own in Canada, have said the same thing about the closing itself: it felt slower than they wanted in the moment, and looking back, it was the right kind of slow. The family has stayed in the home since, and Budi has mentioned the saved amount more than once when helping a friend or coworker think through their own first mortgage decisions.

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