Short answer first. Porting means moving your existing mortgage, rate and terms included, from the home you're selling to the one you're buying, which can save you the prepayment penalty for breaking mid-term. Most fixed mortgages are portable on paper. In practice, ports come with tight timelines and a requalification, and sometimes paying the penalty is genuinely the better deal. Here's how to tell.
What a port actually is
Your mortgage is a contract with a rate and an end date. When you sell mid-term, the default outcome is breaking that contract, and fixed-rate penalties calculated on interest rate differential can run to five figures. A port transplants the contract instead: same lender, same rate, same maturity date, new house. If you kept a great rate from a few years ago, that's real money preserved.
Needing more money? Blend and extend
Most people move up, not sideways, so the new home needs a bigger mortgage. Lenders handle this with a blend: your existing balance keeps its old rate, the new money comes at today's rate, and the two are blended into one payment. It's tidy, but the blend math is exactly where you want independent eyes, because a blended rate can quietly cost more than breaking and taking a fresh mortgage somewhere sharper. I run both versions side by side before recommending either.
A port is a tool, not a default. The only way to know it's the right tool is to price the alternative.
The catch: timelines and requalification
Two things surprise people. First, the window: most lenders give you 30 to 120 days between selling and completing on the new purchase to execute a port. Sell in March, buy in September, and the port may be off the table. Second, you requalify: the lender underwrites your income, credit, and the new property from scratch. A port is not a right, it's a re-application with your old pricing attached.
When breaking beats porting
If today's rates are lower than your contract rate, the penalty may be worth paying to reset at a better rate, especially early in a term. If your lender's blend offer is weak, the whole market is the alternative, and that's a comparison your bank branch won't volunteer. And if your timeline can't fit the port window, the decision makes itself. This is renewal-adjacent territory, so the renewal playbook pairs well with this one, and broker vs bank explains who actually runs these numbers for you.
Frequently asked questions
Can I port a variable-rate mortgage?
Usually not directly. Variable mortgages typically must be broken, though the penalty is normally three months' interest, far smaller than fixed-rate differential penalties. Some lenders let you convert to fixed and then port.
How long do I have to port my mortgage?
It varies by lender, commonly 30 to 120 days between the sale closing and the new purchase completing. The exact window is in your mortgage contract, and it's worth knowing before you list.
Do I have to requalify to port?
Yes. The lender re-underwrites your income, credit, and the new property. A port preserves your rate, not your original approval.