Provisional Cast-on at Underarms [TUTORIAL]

The best part about knitting a seamless top-down sweater or cardigan is when you get to separate body and sleeves. But the underarms… that's where things often get messy. How do you cast on underarm stitches? And more importantly, how do you pick up those underarm stitches so that you don't get any holes?

Usual cast-on methods can often leave gaps, tightness, or awkward stitches to pick up later. In this post I'll demonstrate my favorite method for avoiding all that by casting on underarm stitches provisionally. At the end of the post I'll also share my go-to two-round tip for eliminating any unsightly holes.

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Zingiber was the impetus for switching to a provisional cast-on at underarms.

Why Use a Provisional Cast-on?

The revelation for using a provisional cast-on at underarms came to me back in 2019 when designing the Zingiber hoodie for Making Stories.

Back then, the magazine was in its infancy — the hoodie pattern appeared in Issue 2 — and they had a rather unusual design process: the pattern had to be fully written and tech edited before even the designer was allowed to start knitting the sample. (They later changed the order of operations and have since shut down but that's beside the point.)

Zingiber is a cabled hoodie where the majority of the garment is done in reverse stockinette — purls on the outside. Thinking nothing of it, I'd originally written the sleeve separation instructions using the backwards loop cast-on from which sleeve stitches were to be picked up and knit later on. But the tech editor had a question: would this not mean that the seam where the stitches are picked up from would show up on the right side of the work?

Good question! I pondered this for a moment. Maybe you could pick up and purl instead, moving the seam to the inside? Then a lightning bolt hit: why have a seam at all? What if you could cast on stitches in a way that results in live stitches with no seam, without having to pick up anything? You can probably guess by now that you can: with a provisional cast-on.

A provisional cast-on (PCO) at the underarms has a multitude of benefits.

No picking up stitches required. A provisional cast-on creates live loops going in two directions, casting on both body and sleeve stitches at the same time. Because the underarm stitches are already live, there's no need to pick up anything when it's time to work the sleeves.

There is one small caveat, though: you do need to pick up some extra stitches to avoid underarm holes. But we'll get to that a bit later.

No bulky seams. Because there's no need to pick up underarm stitches, it also means that there are no seams at the underarms. This is great for knitters who have sensory issues or just want to have a smooth, seamless transition from body to sleeves.

Works in any stitch pattern. The provisionally cast-on stitches are just loops on the needle. They're in a superposition, primed to become either knits or purls, but they're neither until they're first worked into. For this reason, a provisional cast-on works in any stitch pattern: stockinette, reverse stockinette, ribbing, lace, moss stitch… you name it.

You can use any provisional cast-on method for this but I prefer the winding cast-on because it's quick, easy, and doesn't require any other tools, notions, or needles besides the ones you're already working with.

Wychwood Cardigan features provisional cast-on at underarms.

How to Cast on Underarm Stitches Provisionally

For this tutorial I'm demonstrating casting on underarm stitches with my upcoming Wychwood Cardigan pattern. The pattern is currently in test knitting, slated for release in July 2026.

Place sleeve stitches on waste yarn.

Here I've transferred all sleeve stitches onto waste yarn, ready to cast on underarm stitches. Next, I'm using the winding cast-on but — instead of a secondary needle — I'm creating new stitches directly onto the same waste yarn that's already holding the sleeve stitches.

Hold onto the working yarn (top) and waste yarn (bottom).

Step 1. Hold onto both the working yarn and the waste yarn.

Wrap the working yarn behind the waste yarn.

Step 2. Wrap the working yarn behind the waste yarn…

Wrap the working yarn under the waste yarn and over the right-hand needle.

Step 3. … under the waste yarn, then over the needle to the back. That's one stitch cast on.

All you're doing is winding the working yarn over the needle counter-clockwise, catching the waste yarn in the process. Hence the name: winding cast-on. If you've ever done toe-up socks, you might be more familiar with the term Turkish cast-on. Same difference.

Continue winding on until you've cast on all underarm stitches.

Repeat steps 1–3 until you've cast on however many stitches the pattern tells you to. Here, I've cast on 8 underarm stitches for my size. The waste yarn runs parallel to the needle on the underside of the newly created stitches.

Knit the first stitch on the other side of the underarm to join.

Step 4. Bring the two needles closer together and knit the next body stitch. This joins the back and front.

One underarm done.

Step 5. Secure the waste yarn by tying the two ends together so that the stitches don't run away.

Now you've got all sleeve stitches and all newly cast-on underarm stitches on the same waste yarn. Repeat the process for the other sleeve: place sleeve stitches on hold, then cast on underarm stitches using the winding cast-on technique onto the same waste yarn.

On the next row, work the underarm stitches normally. They can feel a bit loose at first but that looseness will even out when it's time work the sleeves. Speaking of which…

How to Avoid Underarm Holes

The tricky bit about starting the sleeve is not picking up the underarm stitches — that's easy because they're already live! — but how to avoid those pesky holes from developing at the junction where stitches coming from different directions meet.

Some say underarm holes are unavoidable and can be cinched in when weaving in ends. I say it's better to prevent the holes from appearing in the first place.

Underarm holes appear at the junction where stitches coming from two directions meet.

Here I've placed the sleeve stitches and underarm stitches back onto a circular needle. Starting from the middle of the underarm, I've re-joined yarn and worked to the end of the underarm stitches (right) so that the previously held sleeve stitches are next on the holding needle (left). If I were to now start working the sleeve stitches, that would result in a massive hole.

To eliminate that hole, the solution is quite simple: pick up as many extra stitches on the first round as you need to, then adjust the stitch count on the second round to whatever the pattern says you ought to have. It takes two rounds to get the sleeve going but the results are better than if trying to get to the right stitch count on the very first round.

Picking up only one leg results in stretched-out stitches.

Here's what you don't want to do. Some instructions say to pick up the strands along the edge to use as stitches. But picking up only one leg (half a stitch) will result in long, stretched-out loops.

Pick up extra stitches by knitting into the middle of a full stitch.

Instead, insert the needle tip into the middle of a full stitch below (left) and knit it (right) as if doing a median increase. This gives a much more stable pick-up that is not prone to stretching out.

Pick up as many extra stitches as you need to.

Pick up as many extra stitches as you need to fill the void. I find that 2–3 stitches is usually enough but you can pick up even more if you want. Here I've worked 4 live underarm stitches (half of the full 8) that were cast on provisionally, then picked up 3 extra stitches from the gap.

To finish the first round, work across the sleeve stitches, then repeat the pick-up on the other side of the underarm before working the second half of the underarm stitches.

On the second round, work to last underarm stitch.

On round 2 you want to decrease away those extra stitches that were picked up on the first round. First, work all but one of the underarm stitches.

Decrease extra stitches picked up from the gap.

Then do as many consecutive decreases as the number of extra stitches you picked up. I like to make the decreases lean into each other so SSK for the first one, K2tog for the second, and — since I picked up 3 extra stitches — another K2tog for the third.

Work across the remaining sleeve stitches, again stopping one or two stitches before reaching the underarm stitches. Decrease the extra stitches picked up, then work to the beginning of the round in the middle of the underarm stitches, and place a BOR marker. Now you're ready to start the sleeve in earnest.

Finished underarm.

Any remaining oddities, gaps, or enlarged stitches can be duplicate stitched over when weaving in ends. In the finished garment the underarm looks like this: seamless and hole-free.

A provisional cast-on has the benefit of creating smooth and seamless underarms, works in any stitch pattern, and doesn't result in added bulk at the underarm join. It may feel a bit fiddly the first time you try it but can quickly become one of those tried-and-true techniques you'll reach for again and again. It certainly did for me!

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