Your down payment will influence your monthly mortgage payment amounts as well as your mortgage rate. It works like this: the larger your down payment, the smaller your mortgage, the lower your monthly payments will be. And of course, the opposite is true as well. Moreover, you will have to pay CMHC mortgage insurance if your down payment does not hit 20% of the value of the property you want to purchase. CMHC insurance is an extra expense, added to your mortgage payment, and so it should be considered when you evaluate your mortgage affordability.