That means you are losing 3750 points (25% bonus on United)between 25000 and 40000 miles and potentially 100% of the fractional portion of the next 10000 miles once you have reached the 50 60 70 etc thousand mile leve(it would be a bummer to have 59995 miles for example--you would not get the next 10000 miles. In reality, if you fly enough you come out ahead (slightly) on Air Canada (i.e. if you fly over 50,000 miles). At 50,000 miles on Air Canada you would have earned 10,000 miles extra and only 6250 on United. After 50,000 miles you are sort of on par in each program as long as you are close or a little bit over the next 10,000 miles (see above about the bummer).