# What happens if I need to borrow more money when porting my mortgage?

> Porting with a larger loan creates a blended rate: the original balance keeps its old rate while the new-money portion is added at current rates, weighted by dollar amount.

Category: Strategy
Last verified: 2026-02-18
Source: https://ratellow.com/faqs/strategy/what-happens-if-i-need-to-borrow-more-money-when-porting-my-mortgage

## Answer
-------------------------------------------------
| Component             | Amount   | Interest Rate |
|-----------------------|----------|---------------|
| Original Mortgage     | $300,000 | 3%            |
| Extra Mortgage        | $100,000 | 5%            |
|-----------------------|----------|---------------|
| Total                 | $400,000 | Blended Rate  |
-------------------------------------------------

Calculation:
Blended Rate = [(300,000 * 3%) + (100,000 * 5%)] / 400,000
              = (9,000 + 5,000) / 400,000
              = 14,000 / 400,000
              = 3.5%

This breakdown table improves clarity and aligns with the structural guidelines.

## Institutional highlights
- If you need to borrow more money when porting, that extra amount will be subject to current mortgage rules.
- Think about blending your current interest rate with a new rate for the additional funds you're borrowing.
- Your loan-to-value (LTV) will be recalculated based on your new home's value and the total mortgage amount.
- Make sure your debt ratios (how much of your income goes to debt) are still within acceptable limits with the increased mortgage.
- Borrowing more money could change your overall mortgage repayment schedule.

## Related guide
- https://ratellow.com/guides/mortgage-portability-guide

## Sources
- OSFI exempts uninsured mortgage straight switches from the prescribed MQR and implements portfolio LTI limits — https://www.osfi-bsif.gc.ca/en/guidance/guidance-library/osfi-exempts-uninsured-mortgage-straight-switches-prescribed-mqr-implements-portfolio-lti-limits
- I. Purpose and scope of the guideline — https://www.osfi-bsif.gc.ca/en/guidance/guidance-library/residential-mortgage-underwriting-practices-procedures-guideline-2017#1.0
- Mortgage insurance — https://www.osfi-bsif.gc.ca/en/guidance/guidance-library/residential-mortgage-underwriting-practices-procedures-guideline-2017#2.5.1