I'm looking for informations about calculating ELO (FIDE) rank I'm looking this informations for new app to calculating ELO (FIDE) rank after games (live tournament etc.). So you can predict your future rank before it is pbulished on FIDE site.
Here is a blog post about elo calculation.

You can find the rules for determining the correct K-factor on this site, which also contains an official Fide rating calculator to check your results against.

Here is the official description of the rating calculation (based on tables instead of formulas).