Maintenance

From EU3 Wiki

If you have a standing army or navy, you pay maintenance upkeep. Maintenance can be set anywhere from 100% down to 50% by a slider in the military page of the Domestic Management interface.

Keep in mind that if you set your maintenance to 50% no reinforcements will be sent to your forces.

Also remember that your unit morale will take time to be restored when you return maintenance to full.

If you exceeds your country's force limit, you are penalised with higher maintenance cost. Don't do this unless your economy can handle it. National ideas can increase your force limit.

Mercenaries cost double in maintenance compared to regular troops.