All units in the Skaven army always add their current rank bonus to their Leadership value for any Leadership based test.

First work out the Leadership of the unit as normal (character in the unit, General within 12", magic bonuses/penalties, etc) and then add the rank bonus of the unit to this value. The maximum bonus you can get is obviously +3, for a maximum total Leadership of 10. For example, a unit of Clanrats Id 5) with a rank bonus of +2 will have a Leadership of 7 on its own, a Leadership of 8 if led by a Chieftain (Ld 6) or of 9 if within 12" of a Warlord who is the Skaven General (Ld 7). Note that the General confers his basic Leadership and then the units modify it with their own rank bonus - do not modify the Leadership of the General with the ranks of his own unit and then pass this modified Leadership on to every unit within 12"!

When Skaven lose their rank bonus from a charge in the flank or rear, thev cannot use this Leadership bonus (including when testing for panic for being charged in the flank/rear while engaged to the front). Remember that fleeing units do not have a rank bonus, so fleeing Skaven will have to rally on their basic Leadership.