Imagine there's a sequence of items, it started somewhere in the past and will keep on going. The kind of items could be anything – say days, or football matches, or lectures, or widgets out of an assembly line.

I'd like to refer to the future item that will be, say, the 100th if I start counting them from now. I hope you understand what I mean: the 1st would be the next, the 2nd would be the one after the next, and so on.

How do I denote that future 100th item with a concise expression? I thought of "the next 100th item", but it doesn't sound right.

The problem is that if I just say "the 100th item", that refers to the number 100 since the sequence started, not the number 100 starting counting from now.

Example:

The last 10 widgets were red and blue; the 20th widget from now will be yellow.

Saying "the 20th widget from now" doesn't sound right – but maybe it is? Nor does "the next 20th widget" sound right.

As usual, if possible please also give some references. Cheers!