Why is my decend plan inaccurate?

Well, nothing will be perfect at top of descent because your groundspeed will constantly change.

Personally, I set a target waypoint by which I want to be at 11k or 10k (I don’t plan on descending straight to the cone. Below 10k is a different animal.)

But, in order to account for my groundspeed decreasing I use the following throughout the descent at various times:

(Altitude left to lose * Current GS) / Dist. to Target / 60

This will account for being able to shallow up your descent along the way as you slow down.

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There’s so many ways to determine your TOD.

Personally, not a fan of descent equations as they don’t account for GS variation, are not very realistic, and can get you into terrain trouble. I’ll throw another one at you, courtesy of Captain Joe, TOD is also dependent on your airline cost threshold. Budget airlines descend earlier and more shallow, versus high cost threshold airlines that descend later and more steeply.

Flying for a budget airline (in IF), I start my descent early and shallow, then slightly more steep a few minutes later. My descent lasts about 25-30 minutes (very realistic). I calculate the overall time for each descent step (for each step VS) to FL100. Then I subtract 2-3 minutes from the total time (this is a GS correction factor). Add the time to the waypoint you’d like to be at FL100, and you get where and when your TOD should be. This works flawlessly every time.

Account for STAR altitudes when possible.

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