How does Fertility Work?

[vandevere]

Say, my Ruler has 80% Fertility, and my Spouse has 75% Fertility...

Are there two dice rolls; one for each? Or does the game combine the two Fertility stats to come up with a total of 155% Fertility and dice roll on that?

 

[Anthedon]

http://www.ckiiwiki.com/Breeding gives a general overview. I can't find how exactly the chance is calculated though.

 

[AjayAlcos]

How does Fertility Work?

 

[CrabHelmet]

IIRC, they're multiplicative. The default chance to have a child in a year is 50% (this is set in defines somewhere), if your fertility is 50% and your spouse's is 50%, then you have a 0.75*0.5*0.5=0.125 chance to have a child in a year (so the mean is 4 children for a marriage from 16-45 with default fertility).