Capital moves are subject to an official policy due to the potential for abuse. Please read the relevant section before continuing.
Problems and Costs
Capital moves are expensive and dangerous. They cost 800 gold, or more, and will cause production to drop in both the old and new capital by 50%, control will drop dramatically, and there are affects to loyalty and morale as well. A festival in the new capital will prevent buildings from being used for several days as well.
Reasons to move your Capital
1. Necessity. If you lose your old capital, then you must either reclaim it, or move to a different city/stronghold, in order to recruit troops.
2. Cultural. If your realm reclaims its previous capital, or a city with great historical significance to your realm, then it may make sense culturally to move your capital.
3. Administrative. If your realm is growing, and your old capital sits on one side of your realm, it may make sense to move it to the center of your realm--subject, of course, to the policy restrictions noted above. Move your capital after your war is completed, not in the middle of the war.