It's simple javascript calculating the supply every minute according to :

* Actual number of atomic units is M = 264 - 1. A minimum subsidy may be implemented in the future with <1% annual inflation to preserve mining incentives.
* Uses a recurrence relation. Block reward = (M - A) * 2-20 * 10-12, where A = current circulation. Roughly 86% mined in 4 years (see graph)

You can copy paste the code and run it locally in your browser. The example calculates 525600*26 blocks (see javascript code) ... you can change that to any number you want.

When - what date or what blockheight - would the tail emission kick in ?  

EDIT : 525600*26 = 26 years each year 525600 blocks one block every min.