How long should it take to lose 40lbs?

You should aim to lose about 2lbs a week

I was also like Key, lost 30 lbs in about 3 months by mostly cutting out unneccesary foods. I'm not any where near a fitness/dieting expert, but you may not notice a change because you see yourself everyday. Why not take a picture of yourself each week, or write down your measurements/weight every couple weeks. Also, if you're doing weight lifting, you may be replacing your fat with your muscle you're gaining (if you're doing heavy lifting) - which may account for not having a dramatic dip in weight loss. Don't take that to mean cutting out weights, i only mention this as a possible indicator for not having a dramatic result. Weight loss and excersize are never dramatic like you see on TV. I wouldn't expect to lose more than 3 or 4 pounds a week. You'll probably notice your energy level increasing first, and then other people will notice, and eventually you will. Good Luck!

An average of 1.5 - 2 pounds per week can be achieved using a healthy diet and excercise. This is an optimal expectation for weight that will actually stay off. So 5-6 months minimally.

5 months

Most people because of non linear weight loss, the holidays, cheat weeks etc, take about a year to lose that much.

2 pounds a week... that's 20 weeks... about 4-5 months. Good luck!

11 months

20 weaks-ish