Game rules are configuration choices available when starting a new game that can slightly alter some mechanics. Many such option will disable Achievements.
Difficulty
The difficulty setting can grant players the following bonuses:
| Difficulty |  Hostile Scheme Resistance
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 Fertility
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 Short Reign Duration
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Tyranny Gain
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 Stress Gain
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 Knight Survival
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 Minor Disease Chance
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 Health Boost
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 Faction Formation
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Vassal Opinion
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Liege Opinion
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Achievements |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Very Easy | +30 | +20% | -50% | -75% | -50% | +75% | -75% | Moderate | Significantly Slower | +25 | +50 | 
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| Easy | +15 | +10% | -25% | -25% | -25% | +66% | -15% | Small | Slightly Slower | 0 | 0 |
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| Normal | 0 | 0 | 0 | 0 | 0 | 0 | 0 | None | Regular | 0 | 0 | 
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Gameplay options
The gameplay options can change the game to be less historical.
| Rule | Setting | Effects | Achievements |
|---|---|---|---|
| Exclave Independence | Off | Rulers can have disconnected land anywhere in the world |
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| Limited (AI Only) | AI Rulers at peace will lose disconnected land on succession unless it's part of their de jure territory or is connected to the capital by one county or a naval path. |
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| Significant (AI Only) | AI Rulers at peace will lose disconnected land on succession unless it's part of their de jure territory or is connected to the capital by a naval path. |
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| Total (AI Only) | AI Rulers at peace will lose disconnected land on succession unless it's connected to the capital by a naval path. |
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| Limited | Rulers at peace will lose disconnected land on succession unless it's part of their de jure territory or is connected to the capital by one county or a naval path. |
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| Significant | Rulers at peace will lose disconnected land on succession unless it's part of their de jure territory or is connected to the capital by a naval path. |
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| Total | Rulers at peace will lose disconnected land on succession unless it's connected to the capital by a naval path. |
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| Multiplayer: Murder Schemes | Default | Players can use Hostile Schemes against other players and their families |
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| No Players | Players cannot use Hostile Schemes against other players but can against their families |
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| No Player Families | Players cannot use Hostile Schemes against other players or their families |
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| Minor Diseases | Default | Minor diseases appear as per normal |
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| Fewer | Minor diseases appear 30% less often |
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| Gender Equality | Default | All faiths start with their historical views on gender, clerical gender, male adultery and female adultery doctrines All realms start with their historical gender succession law |
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| Equal | All faiths start with the Equal views on gender doctrine and Either clerical gender doctrine All faiths start with male adultery and female adultery doctrines at the same level (the lesser one) All realms start with the Equal gender succession law |
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| Inverted | All faiths start with their historical views on gender, clerical gender, male adultery and female adultery doctrines inverted All realms start with their historical gender succession law inverted |
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| Regional Heresies | Strict | Heresies are 200 times more likely to be historical if they happen in certain regions |
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| Default | Heresies are more 5 times more likely to be historical if they happen in certain regions |
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| Relaxed | Heresies are random no matter where they happen |
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| Mongol Invasion | Default | An AI character will use the Become Greatest of Khans decision between the years 1180 and 1250 if the player doesn't do it before |
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| Never | Only player characters can use the Become Greatest of Khans decision |
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| Random | An AI character can use the Become Greatest of Khans decision at any point if the player doesn't do it before |
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| Casus Belli Costs | Default | Casus Bellis cost resources |
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| No Costs | Casus Bellis do not cost resources |
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| Culture Conversion Speed | Significantly Slower | The Promote Culture councilor task makes progress 4 times slower |
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| Slower | The Promote Culture councilor task makes progress 2 times slower |
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| Default | The Promote Culture councilor task makes progress as per normal |
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| Faster | The Promote Culture councilor task makes progress 2 times faster |
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| Significantly Faster | The Promote Culture councilor task makes progress 4 times faster |
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| Faith Conversion Speed | Significantly Slower | The Convert Faith in County councilor task makes progress 4 times slower |
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| Slower | The Convert Faith in County councilor task makes progress 2 times slower |
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| Default | The Convert Faith in County councilor task makes progress as per normal |
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| Faster | The Convert Faith in County councilor task makes progress 2 times faster |
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| Significantly Faster | The Convert Faith in County councilor task makes progress 4 times faster |
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| Diplomatic Range | Restricted | Diplomatic Range is reduced by 25% |
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| Default | Diplomatic Range remains unchanged |
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| Unrestricted | Characters can interact no matter the distance |
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| End Date | 1453 | The game will end in 1453 |
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| No End Date | The game will never end |
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| De Jure Requirement | On | Every 5 years titles with de jure land will be destroyed if their holder controls none of their de jure land |
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| On (Limited) | Every 5 years titles with de jure land will be destroyed if their holder controls none of their de jure land unless it's a player's primary title |
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| Off | Titles with de jure land can only be destroyed manually |
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| Custom Kingdoms | On | The Found a New Kingdom and Found a New Empire decisions are available |
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| Off | The Found a New Kingdom and Found a New Empire decisions are not available |
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| Generate Families | On | Landed characters with no recorded family will start with a spouse, a valid heir, a second child if the mother is over 25 and a third child if the other is over 33 |
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| On (AI Only) | Landed AI characters with no recorded family will start with a spouse, a valid heir, a second child if the mother is over 25 and a third child if the mother is over 33 |
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| Off | Landed characters with no recorded family will not start with any family |
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| Same-Sex Relations | Default | All faiths start with their historical same-sex relations doctrine |
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| Accepted | All faiths start with the Accepted same-sex relations doctrine |
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| Sexuality Distribution | Default | Characters have a 89% chance to be heterosexual, 5% chance to be homosexual, 5% chance to be bisexual and 1% chance to be asexual |
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| Bisexuality | Characters have a 89% chance to be bisexual, 5% chance to be homosexual, 5% chance to be heterosexual and 1% chance to be asexual |
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| Homosexuality | Characters have a 89% chance to be homosexual, 5% chance to be heterosexual, 5% chance to be bisexual and 1% chance to be asexual |
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| Asexuality | Characters have a 89% chance to be asexual, 3.6% chance to be homosexual, 3.6% chance to be bisexual and 3.6% chance to be heterosexual |
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| Equal | Characters have equal chances to be heterosexual, homosexual, bisexual and asexual |
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| Faith Acceptance | Default | All faiths start with their historical views on other faiths |
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| Full | All faiths start with the Full Tolerance special doctrine |
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| Randomized Faiths | Off | All characters and counties start with their historical faith |
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| On | All characters and counties start with a random faith |
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| Random Ruler Placement | Off | All rulers have start with their real historical titles |
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| On | All rulers have start with random historical titles |
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| On (Conversion) | All rulers have start with random historical titles and convert to the faith of their primary title's capital |
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| Character Nudity | Default | Characters will appear naked in certain events or if they follow a faith with the Natural Primitivism tenet or are Court Chaplains or Zealous and follow a faith with the Naked Priests doctrine |
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| Never | Characters cannot appear naked |
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| Hungarian Migration | Historical | An AI character will use the Prepare to Cross the Carpathians decision between the years 890 and 910 if the player doesn't do it before |
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| Random | An AI character will use the Prepare to Cross the Carpathians decision between the years 872 and 910 if the player doesn't do it before |
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| Immediate | The Mogyër Confederation starts having used the Prepare to Cross the Carpathians and in a war against the Kingdom of Bulgaria using the Migrate to Pannonia casus belli |
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| Player-Only | Only player characters can use the Prepare to Cross the Carpathian decision |
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Ironman
Ironman is a special game rule that disables character switching and manual saving. The game is saved automatically once every 6 months as well as when exiting the game. Achievements can only be obtained in Ironman mode. In Ironman mode, the game over screen only has the option to exit to the main menu.