How to sew a quick swayback alteration

As much as I love sewing up a garment from scratch, when I find an interesting ready-to-wear item for a good price I get excited. I like to find clothing that is off-the-rack and adjust it to fit me like a custom-made garment. Also, sometimes the clothes we already own just need a little love from the sewing machine to take them up another level or keep them out of the donation basket. One of the most common adjustments I end up making to my clothes is a swayback alteration. Swayback wrinkles are located at the center back waistline and fade to nothing at the side seams. For my body, a combination of anatomical features contributes to the characteristic horizontal wrinkles at my back waistline. No matter the cause of these wrinkles, in this blog post I will show you a quick adjustment your favorite top to correct for a swayback.


Step 1 – Start with a shirt

I will walk you through the process with a top that I just altered. The top I purchased is a lightweight workout top. Here is a picture for reference.

I was excited when I found this top. The neon orange color was one that coordinated with some of my favorite workout bottoms, and finding a matching mesh would be nearly impossible if I had wanted to make this garment for myself. I love the overall not-tight, not-loose fit, the fun mesh details, the curve of the neckline, the rolled sleeves, and the raglan shoulder seams. Also, from the front, the fit of this top was great.

Step 2 – Locate the wrinkles

The only thing I didn’t like about this top was the puddle of wrinkles at the back waist. My own anatomical combination of short torso length, larger bust size, straight upper back, and actual swayback dip in my lower back all contribute to these wrinkles. Although, as you can see from the photo, there are other wrinkled areas in my outfit. For example, the underarm area, and under my bum at the top of my legs both have some wrinkling. These wrinkles, though, don’t bother me as much. With a raglan sleeve, extra fabric at the underarm is unavoidable and adds the mobility I want in an athletic shirt. As for the leg wrinkles, totally eliminating these on my body type is almost impossible, even on my custom leggings, so I accept them to a certain degree.

So, although the swayback wrinkles aren’t drastically offensive, they are: a.) just annoying enough to bother me, and b.) easily remedied with a swayback adjustment. I will show you how I do this quick fix. Let’s get started!

Step 3 – Pin out the excess

First, you can start by putting the top on with a sports bra, or whatever you’ll usually be wearing under it. Put the shirt on inside out; this is just a little shortcut for a quick alteration like this. Next, pinch up the excess fabric at the bra-band level. It is important to pinch the fabric up here, even though it might seem counter-intuitive. While the actual puddling of fabric is closer to the waist-level, the excess typically originates from this area. Reaching and pinning behind your own back can a little tricky to do by yourself, but remember, it doesn’t need to be perfect. Just pinch up, usually about 1/2″ (1.27cm) of folded fabric as close to the center back as possible. Pin that fold with a safety pin or sewing pin.

Check your back view in the mirror to be sure that you have pulled up the right amount of fabric. You will know if you pulled up too much because the back hemline won’t look even. It will look pulled up in the middle. If you didn’t pull up enough excess, you will still have puddling of fabric at the back waistline. Adjust as necessary.

Once you are happy with the center pin, take another pinch of fabric, roughly halfway between the center pin and the side seam at the same bra-band level. This pinch should be approximately half as much fabric as the first. Again, check the hem for straightness, and adjust accordingly. You only have to pin up one half of the back. Now you can carefully take the top off and lay it out on a table.

Step 4 – Mark it up

Next, you’ll want to smooth your shirt out on a table, and carefully mark your pin locations with chalk or a pencil. Keeping the pins in the shirt, fold the shirt into itself at the fold you just pinned into your shirt. It’s like you are turning your shirt back to right-side-out but stopped halfway through the process. Be sure to measure the distance from the underarm seam to the fold on the pinned side of the shirt. Now, neatly smooth the fold of the shirt accordingly so both side seams match this measurement.

Now, you’ll draw the stitching line. Carefully take the pins out, and draw a straight line through your center pin mark, extending it about 3-4″ (7-10cm) on either side of the center mark. For the next step, use a french curve to draw a smooth line from the straight line you just drew, through the second pin mark, fading to nothing at the side seam. Repeat for the other side of center.

Step 5 – Sew it up

You now have your stitching line marked on your shirt. Next, you’ll want to pin the fabric along the fold and on the other side of your chalk line to hold it in place. Now you’re ready to sew it up! If you use a serger, the seam will have stretch built-in, and the serger blade will cut the excess fabric in one step.

If you don’t have a serger, you can use a short, narrow zig-zag to keep some stretch in the seam. You can also go over the seam twice for added “insurance” in case you pop a stitch. Once you sew the seam on the sewing machine, you’ll be ready to trim the seam allowance down to 1/4″ (64mm).

Step 6 – Try it on

Yay! You did it! Try your shirt on and see the difference! Here is a before and after of my shirt. You can see what a difference this simple alteration has made. The silhouette is so much smoother, and the new stitch line blends in with the rest of the design.

I am so happy with the results of this quick alteration. While it has held up well during my workouts and in the washing machine, you’ll still want to avoid excess stress on this new seam when putting the shirt on or taking it off. The seam won’t have as much stretch as the surrounding fabric. Treating the seam with care is definitely worth the trouble for the difference in fit it makes. If you are nervous about trying this on a brand new shirt, try practicing on an old t-shirt first. I hope you can try this out and have equally happy results!

4 thoughts on “How to sew a quick swayback alteration

  1. Thank you very much for sharing this. It was a gamechanger for a garment. I forgot to do it in the pattern. It is touch a big Solution!

    Big hugs from Germany

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