Hey, I can’t remember if anyone mentioned that there’s also an “add 1NM for every 10kts” you will need to lose” rule of thumb on top of your TOD calculation.
Ex. If you need to be 250kts by 10,000ft and you are at FL400 descending at 300kts:
40,000 - 10,000 = 30,000
Shortened to 30 x 3 = 90NM
Plus,
300kts - 250kts = 50
50 x 1NM/10kts = 5NM
So, 90NM + 5NM = 95NM
It could be argued that, unless you want to use gear to slow down (assuming a pretty standard jet gear limit of 250kts and a common min “clean” speed closer to 200kts, you could also add that second 5NM to take you from 250kts to 200kts when you are ready to configure.
Same comment as before about rules of thumb. It’s just a starting point. 