This article is considered accurate for the current version of the game.
A core is a province that is considered a rightful part of your state. Cores give several strategically important benefits:
- Provinces without a core add to your overextension (unless it's an overseas colony), proportional to their tax base value.
- Core provinces get a +75% positive tax modifier.
- Provinces with cores will have lesser chances for revolts.
- You always have a casus belli if one of your core provinces is occupied by another power.
Coring is the act of adopting a province into what is considered one's patrimony, or rightful homeland. Cored land is not considered conquered or occupied but rather a rightful part of a realm.
Coring is an action which costs administrative monarch points. The amount of points needed and therefore time it takes to core a province depends on:
- Base cost depends on base tax: for each 1 base tax, it costs 20 AMP for provinces with an accepted culture, and 36 AMP for an unaccepted culture.
- An overseas province of your own culture (such as a colony) costs 10% of the normal cost to core. This is to encourage settling the New World and represents how colonies were not regarded as "conquered" or "taken", rather as claimed land.
Coring costs do not depend on:
- Your current overextension.
- The distance from your current cores.
- Your current stability.
- If you are at war or not.
 Reducing core costs
The following national ideas reduce core-creation costs:
- Administrative: Adaptability
- Ottoman tradition:
- Scotland: Pass the Act of Revocation
- Timurid tradition:
- Italy: Path to Citizenship
- Ethiopia: Expansionist Policy
- Dai Viet: Don Dien
- Hordes: Tradition of Conquest
- Theocracies: Church Administration
- Anatolian Beyliks tradition:
- Maratha: Office of the Peshwa:
 Enemy core creation
The following national ideas increase coring costs for a foreign power if they conquer provinces from a nation which possesses this modifier:
- Aristocracy: Local Nobility
- Hungarian tradition:
- Bohemia: Czech Nationalism
- Dai Viet tradition:
- Brittany: Legacy of Breton Independence
- Berber tradition:
- Rajput tradition:
- Italian: Italian Aristocracy:
 Other cost modifiers
- Having a claim on the province reduces cost by 25%.
- War exhaustion: Every point of WE increases cost by +3%
- Overseas provinces of the national culture cost only 10% to core.
Coring is not instant. It takes 3 years, not counting any modifiers, to core a province. All the while you still have the overextension penalties to cost of stability and to your revolt risk. Larger countries core province much more slowly, as each non-overseas province you own will increase coring times by 4%. This sets a soft limit to your country size, as eventually it will take prohibitively long to core provinces. As an example, at 100 province it would take 3 * (1+100*0.04) = 15 years to core a single province. The time to core a province is capped at 20 years.
When the province is occupied by rebels or a foreign power, the coring process is halted until the siege is lifted. As of Patch 1.2, coring progress is also suspended when at war with a country which already has a core in the same province. Coring resumes after the war concludes.
It is not possible to core a province
- while being at war with someone who also has a core in that province
- while there is a missionary converting the province
- while the culture of the province is being changed
 Gaining cores through other means
In addition to coring newly acquired provinces manually, a nation can also gain cores by diplo-annexation of vassals or integrating a junior partner of a personal union. Both processes automatically give cores on all provinces of the acquired territory, making the strategy of "feeding" vassals with uncored provinces a viable strategy to save monarch points.
 Losing cores
- When negotiating a peace deal, a core can be removed through demanding to revoke core.
- Cores in uncontrolled provinces will disappear some time after the most recent of these events:
- The province changed ownership.
- A war between the current owner and the nation owning the core was fought.
- The owner of the core lost ownership of the province.
- The time to lose a core depends on the province's culture relative to the core:[Needs verification]
- 250 years if the core is the primary tag for the province's culture.
- 100 years if the core shares a culture group with the province.
- 50 years otherwise.
- The time is doubled if the core's owner does not exist.
- If a country is destroyed, it loses all wrong-culture group cores.