Companies that produce clothing take in the most profit by catering to the average, to the majority. To this end, most clothes bought in stores do not fit most bodies perfectly well, and tailors find themselves with plenty of business. The job of taking in the waist on a pair of pants, which also fixes most skirts as well, is easily completed by a tailor. Nonetheless, the alteration requires relatively little effort, possibly due to the frequency of the problem, and with the use of a few tools any individual can take in the waist on their clothing.
Remove the rear belt loop in the center of the pair of pants if a belt loop is there. Use the seam ripper to tear out the seams which affix the belt loop to the waistband and set the belt loop aside to sew back on later.
Put the clothing onto the wearer to get a sense of how much material on the waist needs removal.
Take off the clothing and use a fabric marker on the inside of the clothing to mark a line on either side of the rear center of the waistband where you think the new seam should begin. When marking the two lines, draw them as gradual curves which meet the clothing’s center seam just past the waistband.
Rip out the center rear seam to a small amount just past where your marker lines meet the seam. Also remove the seams which connect the waist band to the rest of the clothing for only 2- to 3-inches on either side of the center rear.
Pull the back of the clothing in to where the cloth will sit for the new seam. Thread your sewing machine with thread appropriate to the material of clothing. Sew a backstitch at the beginning of the line of stitching that initially forms the new back seam.
Sew a straight stitch up the seam to the waistband and end with another backstitch.
Repeat the process with the sewing machine to stitch another line of stitching 1/8-inch away from the first line of stitching for added reinforcement. Use scissors to trim excess fabric edges.
Rip out the seams on the waistband below where the back belt loop might sit, or cut the waistband at the center.
Pull in the waistband to fit and use the sewing machine to sew the waistband back together. Trim the excess fabric once again, and run the sewing machine to stitch the waistband back to the rest of the clothing.
Run thread through a needle and hand-stitch the belt loop back in place.