Everyone's weight fluctuates from time to time, but that doesn't mean you have to toss out your favorite pair of pants. If your problem is tight-fitting pants, there are many easy at-home methods to make them looser. The easiest materials to stretch out are denim and cotton. You can try these tricks with most any fabric, and although you may not be able to make the pants as loose as you'd like, you'll definitely be more comfortable in them.
Wash your pants in cold water only. Hot or even warm water will cause the fabric to shrink even further.
Remove your pants as soon as possible when the wash cycle is finished.
Hang the pants by placing pins along the waistline. Stretch out the waistline as far as it will go when you're pinning. Take the time to stretch out the pant legs as well, taking care to smooth out the wrinkles and stretch out the fabric in trouble areas.
Put the pants flat on the ground after about 30 minutes of air-drying. Put one foot inside the side of the waistband closest to the floor and pull the other side up toward you. Stretch the waist as much as you can repeatedly. Flip the pants over, and do the same with the opposite side.
Put the pants on. They should still be damp. Walking or jogging in place and doing some stretching also helps. Do deep knee-bends, thigh stretches and hurdle stretches to loosen up your pants.