Most mortgages come with pre-payment previleges (e.g. upto 20% of the principal in any 12 month period). Since mortgage interest is not tax deductible in Canada, making a pre-payment is a very smart move, especially in the early years of a mortgage. When a pre-payment is made, it immediately reduces the principal balance on the mortgage. The interest portion of future payments also decreases. It is equivalent to getting a tax-free guaranteed return on your money.
Let us assume a $150,000, 5% mortgage, amortized over 25 years. Let us also assume that we pay an extra $150 every month. Over the life of the mortgage, we can save more than $30,000 and become mortgage-free 6 years earlier. A very useful mortgage payoff calculator can be found at Dinkytown.net.