As much as I love the afterthought heel I know that not everyone is convinced and one of the most common questions I hear is from knitters who worry that they won’t know where to place the heel to ensure a good fit.
This is one of the most common concerns and is heard a lot with toe-up sock knitting in general.
With cuff down socks it is very clear. You knit the leg until you have a length you are happy with - for me it’s 6.5”, for my husband it’s 7.5”. The you knit the heel, then you work the foot.Simples!
With toe-up socks it is more of a leap of faith. Standard instructions tell you to start the heel between 2-2.5” before the back of the heel ie total foot length minus 2 to 2.5”. If you get to the leg and find that the heel is in the wrong place, then a bit of judicious ripping is required.
With an afterthought heel this is a rather more unnerving prospect as once your heel is cut, there isn’t much room for error.
The best advice I can give for this, which will also increase your confidence, is to practice doing a few standard toe-up socks first with either a basic short row heel or a fish lips kiss heel. Learn where the best fit point is for you - you can put in a lifeline if needed so that if you do make an error in the heel placement you can just rip back to the lifeline and not worry about lost or dropped stitches.
Make a careful note of the exact length for your ideal heel placement then use this measurement when doing your afterthought heel.
Also - my best tip for making sure you get a good fit is rather than measuring the toe-up sock flat, actually slip it onto your foot and use a bulb pin or similar to mark the point on the base of the sock where the cut should go. For my UK size 6 foot, this is usually at 7.5” from the toe (with sock slightly stretched). My total foot length is 9.75”
Armed with this information I can now pretty much pop in an afterthought heel (for me) wherever I am, safe in the knowledge that the sock will fit me fine.
I hope this helps ease the nerves somewhat. If you do decide to be brave and give it a go - do let me know how you get on.