Whether it's a vintage find from a thrift store that wasn't your size or you have recently lost weight, you may find yourself needing to take in a favourite jacket to make it fit. A tailor can complete this alteration for a price, but the actual procedure is easy enough for a beginning sewer. Practice on inexpensive oversized jackets or thrift store finds before altering higher-quality jackets, so you can learn in case something goes wrong.
Turn the jacket inside out. Try it on to gauge how much smaller you need to make it.
Gather the fabric along the side seams of the jacket until it is pulled to your desired size. Pin the excess fabric to hold it separately from the rest of the body. It should now fit and have two strips of excess fabric pinned out from the jacket down each side seam.
Remove the jacket and lay it still inside out on a flat surface. Sew along the pinned line up each seam of the jacket. Remove the pins only when the stitches are secure.
Cut away excess fabric along the new seam to complete the alteration. If you think you may need to let the jacket out again in the future, skip this step.
Use a seam ripper to separate the lining from the sleeves. Remove the original stitches.
Try the jacket on and fold the sleeves under to the newly desired length. Hold the fabric in place with pins that are long enough when you move your arms.
Remove the jacket and turn the sleeves inside out. Firmly press the new hemline and stitch along it. Make sure the lining is out of the way. You will reattach it in the next step.
Remove any excess lining. If you have shortened the sleeves by an inch or less, leave it: it will not affect the jacket's fit and is not worth the risk of an erroneous cut.
Stitch the lining back to the jacket sleeve. Turn the sleeves right-side out and make sure all your stitching and sleeve lengths are even.