You don't have to part with your favourite pair of jeans, even when they start feeling a bit snug. It's easy to make the waist of those jeans a little bigger so you can still wear them with style.
Determine where you'll add the extension in your waistband. It's usually best to put one on each side.
Measure your waist to decide how much of an extension you need. This method works for small enlargements -- nothing bigger than 5 cm (2 inches).
Once you have that measurement, divide it in half. If you need 2.5 cm (1 inch) more space in your jeans, you'll make a 1.2 cm (1/2 inch) extension on each side.
Cut the elastic tape into two pieces about 1.2 cm (1/2 inch) longer than you decided you want the extension to be.
Measure your jeans' waistband where you want to put the extension. Measure a section that's half the size of what you want your extension to be. Let's say you want your waistband to be 2.5 cm (1 inch larger). You'll extend it 1.2 cm (1/2 inch) on both sides. So make this measurement half of that and mark off a 6 mm (1/4 inch) wide section on each side.
Cut out this marked section of your waistband in a V shape. Cut from the top of the waistband to the seam down at an angle to form the first side of the V. Then cut the next side of the waistband from the top to bottom seam to form the second side of the V. Do this on the other side of the jeans, where you'll also add the extension.
Turn your jeans inside out to sew the elastic in place.
Place one piece of elastic tape on one section of the jeans. Place the tape so that it's flush with the top of the waistband and so it's 6 mm (1/4 inch) in from the top edge of the cut. Use a straight pin to pin it in place. Pin the other end of tape to the other side of the V cut the same way. Pin that end in place.
Use a sewing machine to sew the elastic onto the waistband. Sew straight down from the top of the elastic tape to the bottom, ensuring it's securely attached to the jeans. Do the same on the other side of the V cut.
Repeat Steps 8 and 9 on the other side of your waistband, where you'll add your second extension.
The elastic will be visible but can be covered by a long shirt or thick belt.