A curved seam allowance has the wrong amount of fabric in it once turned, and clipping or notching is how you correct that. Which one you use depends on which way the curve goes.
Clip inward curves. A neckline or an armhole curves inwards. When the seam is turned, the allowance has to spread out to cover a longer line, and it cannot — so it pulls the seam tight. Cutting small snips into the allowance, at right angles to the seam, lets it spread. Clip almost to the stitching, leaving one or two threads.
Notch outward curves. A collar edge or a pocket curve bulges outwards. Turned, the allowance has too much fabric for the space, so it bunches into ridges. Cutting small wedges out of the allowance removes the surplus. Same rule: close to the stitching, not through it.
How many. As many as the curve needs and no more. A tight curve wants clips every 5 to 10 mm; a gentle one every 20 to 30 mm. Each clip is a weak point, so do not do it for the sake of it.
On corners, trim across the point rather than clipping, and taper the allowance on each side.
On fabric that frays, stagger the clips on the two allowances so they do not line up, and consider pinking rather than straight cuts.
Straight seams need neither. Clipping a straight seam does nothing except weaken it.
Press over a curved surface afterwards, so the shape survives rather than being flattened out.
Questions people actually ask
How close to the stitching can I cut?
Within a thread or two on stable fabric. Leave more on anything loosely woven, and stagger the cuts between the two layers.
What if I cut through the stitching?
Sew a short reinforcing line just outside the original seam over that section, then trim. Do not simply leave it.
Last reviewed 2026-08-11