Most mortgages have a length of 15 or 30 years. While some companies do offer 20 year mortgages, the interest rates for 15 and 30 year mortgages are fixed. Because of this they are used more often than mortgages which last 20 years. If you choose to take a 15 year mortgage, your monthly payments will be much higher. This will mean that you will have less income available to save. A 30 year mortgage will give you lower monthly payments, and will allow you to save more money than you would save with a shorter mortgage.