Have seen this numerous times.....
"Feed 2-3% of his adult body weight
This is easier to determine if you have a purebred dog, but the amount you feed should be 2-3% of your puppy’s anticipated adult weight. If you’re not sure what that will be, then feed about 10% of his current weight. Watch to see if he gets too fat or too thin and adjust accordingly."
10% for a puppy weighing 40 lbs seems way too much... 4 lbs per day is feeding at a rate of an anticipated adult weight of 160lbs.
Make an assumption for adult weight .....perhaps 75 lbs....that would be 1.5-2.25 lbs per day averaging 1.9 lbs.
The general consensus suggests keeping them a bit on the lean side while their bodies are still growing.....