For some insane reason, I have a terrible problem calculating the length of top down socks. I’m always completely paranoid I will run out of yarn on the leg, so by the time I’m sewing up the foot, I end up with more yarn leftover then is necessary.
Currently I’m knitting myself a pair of cashmere/silk/alpaca socks two at a time and I’m just about to start the foot decreases, which means I will be left with a ridiculous amount of yarn. These socks have a cabled design running all the way around them, but they do have just five rows of ribbing at the top, so my question is, is it possible to cut a stitch at the top and start knitting the ribbing again to make the top of the sock more substantial and use up the rest of my super amazing yarn?
You can definietly do it with St st, so I’m sure its doable with ribbing.
You can pick up a row of sts 1-2 rows in from the CO (this will be a bit harder with ribbing than with St st), then cut the initial CO st/sts. You’ll have to unweave/unknot those 1st 1-2 rows to get to where your picked up row is (unfortunately, you can’t easily frog from the CO end) but then you can knit as usual adding the length you desire. Because the sts are going the opposite way (toe-up rather than cuff-down) they will be slightly offset on the 1st worked row (this will likely be more obvious in ribbing than in St st but you can call it a design element).
A future option would be to start with a provisional cast on. If you have lots of yarn left, just pick up the live stitches and knit the top longer. If you don’t have lots of yarn you can use the live stitches for binding off.
Here’s a video from the incomparable Eunny Jang for lengthening (or shortening) your knitting. Towards the end, she demonstrates how to pick up sts over knit and purl sts. Fortunately, knitting in the round means that you don’t have t o worry about the offset of sts as she shows. Good luck with it! The technique works beautifully.
Another way to avoid this problem would be to knit socks toe up. That way, you do the toe first, then the foot, heel, and once you start the leg you can just keep right on knitting until either the socks are the same length, or until you run out of yarn. 
WolfWalker, that’s my solution too. I’ve had to redo too-tight BOs more than once, going back to redo a too-tight CO would be too disheartening.
I LOVE this idea! For some reason I love top down socks but it never occurred to me to do a provisional cast on. I will have to remember this in the future. You, my knitting friend, are a genius!
For now I will try the method described by Eunny Jang. These socks are starting to feel like a job!
