Gavelkind is a succession law where land is divided among the ruler's children.
The eldest inherits the primary title and becomes the new player character. The deceased ruler's other titles are distributed among all eligible children in a roughly equal manner. Junior heirs become vassals (or independent rulers, if they inherit equal-tier titles).
Gavelkind is probably the most difficult succession law to master. It requires some knowledge to benefit from its advantages, without suffering too much from the increased risk of succession wars from siblings who now have both claims and armies.
Availability
Gavelkind is the initial succession type for most feudal realms. It is easily available, having no crown authority / administration/ technology requirements. Gavelkind is also a faction favorite; weak rulers will often be forced to adopt gavelkind by their vassals.
For tribal rulers or unreformed pagans, gavelkind is one of the few succession types available. Their only other choice is usually elective gavelkind, which is widely seen as inferior. (Rulers who are both tribal and unreformed pagan are further restricted and can only use elective gavelkind.)
However, 
Muslim tribal rulers may use Open succession, Celtic cultures (or characters with relevant 
bloodlines) may use Tanistry, and African/Romuva tribal rulers can use Eldership. With 
Conclave, most feudal realms will be able to use feudal elective once they pass the "council authority" law, at the price of locking in feudal elective as the only succession type while full council authority stands.
Advantages
Gavelkind reduces faction revolt risk in several ways:
- Rulers may hold a 30% larger demesne, giving them the potential to be more powerful relative to their vassals.
- Rulers get +5 opinion with both dynastic and non-dynastic vassals (an advantage shared with Tanistry).
- Factions to change succession law are much less likely (an advantage shared with Feudal elective).
Gavelkind also prevents the prestige penalty normally incurred for having unlanded adult sons.
Disadvantages
Gavelkind creates the perfect conditions for a succession crisis. The primary heir can lose a large portion of their demesne and may even be reduced to a single county. Meanwhile, the new ruler's siblings have inherited both claims and land, allowing them to create factions demanding their own installation.
Gavelkind discourages rulers from taking actions that might otherwise be advantageous, such as having many children or holding many titles; this means that forming an empire while under gavelkind requires the character to stockpile both gold and piety in order to create the second kingdom title and the empire title at the same time.
Gavelkind has several restrictions to prevent cheesily giving your eldest child everything:
- You cannot destroy titles subject to gavelkind succession (except titular titles).
- You cannot give your primary heir more than a single county. That is, you cannot grant them a duchy title or a second county. (You can, however, strengthen them by granting extra castles or tribes.)
- Furthermore, you can only give your primary heir a county that they are expected to inherit.
- Christians cannot disinherit any[?] heir by making them a bishop.
Details
Heir selection
The eligible children are determined by gender law. Agnatic-cognatic gavelkind uses a strong form of male preference: when there are both sons and daughters, only the sons will inherit.
With gavelkind succession, dead characters do not "placehold" as they do under primogeniture. If your firstborn dies, you can expect your second son to inherit rather than an unready grandson.
This Reddit thread gives more details.
Creation of claims
As with any succession law, all of the deceased ruler's children get claims on all of the top-tier titles.
When junior heirs become vassals, this means they have claims against their liege, allowing them to create claimant factions. The liege does not get claims against their vassals. (This is good, because such a claim could only be used to unfairly revoke the vassal titles).
When multiple heirs become independent of each other (due to the deceased ruler holding multiple top-tier titles), they get claims against each other. Often, one will declare war on the other using the Claim or Claim All CB, attempting to reunite the titles (at least until the next succession).
Title division
The equal partition of land is flawed by the fact a vassal can only have one liege in the game. So due to intermediate Duke/King titles, it results in both titles and land being unequal.
The exact algorithm is unknown, but:
- Each eligible child receives one title in birth order until all children have a title, at which point it wraps back around to the oldest.
- If one title is higher in rank than others (only one duchy, multiple counties), then the younger children become vassals of the main heir.
- Titles given out prior to succession are taken into account. A child given 3 titles already sits out three rounds of inheritance.
- As of patch 2.3.4, children who would inherit only an empire, kingdom, or duchy title but no counties are automatically given the de jure capital county of the top level title to ensure that they qualify to inherit. Also, any baronies that are not county capitals are now distributed in order to make children eligible to inherit.
- Titles are weighted by their rank. The game tries to give out empires then kingdoms then duchies as evenly as possible.
- The game favours titles being given out into politically logical portions. If multiple duchies and multiple counties in a duchy are inherited, the game tries to prevent dividing duchies or higher as much as possible.
- The game favours giving the most powerful (in terms of levy strength) titles to older children, all other factors being equal. The capital county of an independent nation has a +50% levy strength bonus, making it most likely to go to the eldest.
- Nobles of the same rank cannot be vassals of one another.
- If the ruler's titles are of equal rank and vassal of a higher-ranked ruler, they become distinct vassals; i.e. multiple duchies will be divided among multiple heirs who will all become vassals to the same king.
- If the ruler's titles are of equal rank and he was independent, his realm will be split into independent realms among his heirs.
- Vassals go along with whichever title they were vassalized to. This usually means counties going with their duchy, but the primary duchy will usually inherit vassals from incompletely controlled duchies.
- All gold and retinues go to the main heir, giving an advantage in reunification wars.
- This forum thread claims to have cracked the title division algorithm in more detail.
To give an example, if a duke has 3 duke-level titles, but only 2 actual counties, an eldest daughter and then three younger sons, then only the eldest two male children inherit under agnatic-cognatic gavelkind. The older son gets two duchies and a county; the middle son gets one duchy and one county; the third son gets nothing because he cannot inherit any higher titles without at least a county; lastly, the daughter does not inherit anything because she has brothers. If the two counties are in different duchies, then the oldest son gets the duchy with the county that has the largest levy, and the younger inheriting son gets the duchy that has the remaining county. The younger inheriting son is no vassal to his older brother because they are of equal rank. The youngest son and the daughter remain courtiers of their oldest brother, provided they were courtiers before.
Opinion
A ruler under gavelkind succession will face the following opinion modifiers:
| Character | Opinion modifier | Reason |
|---|---|---|
| Child who is primary heir | -5 | They would certainly prefer primogeniture! |
| All other children set to inherit | +15 | Almost certain of getting something out of the succession. |
| All other dynasty members | +5 | |
| All vassals | +5 | A divided realm increases their own dynasties' future prospects. Vassals like decentralized and weak states in general. |
Historical basis
Partible inheritance was a common practice in early feudal realms. It took many forms, including several that were called "gavelkind". Gavelkind as a historical form of inheritance was found in Kent, Ireland, Wales and some parts of England.
The effects can be seen in various start dates:
- In
769, we see the brothers Charles and Carloman vie to reunite Francia. History was slightly more ambiguous: their father hoped they would rule as "joint kings" rather than each ruling a fully independent half-kingdom. - In
867, we see the legacy of Charles' success. What was briefly his "Holy Roman Empire" is now six independent kingdoms, each ruled by a different descendant: West Francia, Lotharingia, East Francia, Aquitaine, Italy, and Bavaria; his empire had fractured after the death of his son, Louis the Pious. - In 1066, we see the descendants of Rurik (Rurikid dynasty) holding many independent duchies in Rus and Ruthenia (although actual Russians did not use gavelkind; they had the so-called "rota collateral" succession system, which is closer to seniority in many aspects. Indeed, the succession of the kingdom of Kievan Rus in-game is Seniority in 1066. After the Council of Liubech in 1097, rota was abandoned and replaced with appanage, which is basically gavelkind).
Strategies
Arranging to have a single heir
Disqualify younger siblings from inheritance:
- Send them to a monastery
- While they are not heirs to any title, e.g. while your demesne only has 1 county
- Or while you have them imprisoned, perhaps after excommunication.
- Send sons to a holy order
- Unless you're pagan (Muslims do not use gavelkind), granting them a theocratic title will disinherit them. You are not allowed to disinherit your primary heir in this manner, although you can do it to your heir's heir. If Catholic, they may have the opportunity to become Pope, increasing dynasty prestige. In case your heir dies unexpectedly, you can revoke the church title of one of your other sons to put him back in the line of succession.
- Give them a newly constructed church holding
- Give them a church freed from infidels via holy war
- With free investiture, nominate them as successor to an old or accident-prone bishop.
Allow your titles to pass between branches of your dynasty by not having any children, but allowing other dynasts to breed. Dynasts having multiple eligible heirs will not split the titles. Educate dynasts' children in your court.
- This strategy works best if your dynasty has several branches which are landed so that breeding can proceed without inhibition.
- Ensure that your dynastic heir doesn't have children of their own before inheritance. Consider monitoring other members in the line of succession as they can become heir due to untimely deaths.
Kill unwanted heirs:
- Imprison and execute (generally results in tyranny and
)
- If you're in the Byzantine culture group, you can castrate them instead, avoiding Kinslayer and tyranny at the cost of a large opinion penalty. Eunuchs can't be given or inherit landed titles. Do this before they have children, otherwise they will inherit instead. (needs verifying)
- Send your sons to lead the troops, and try to get them killed in battle or by disease.
Consider trying to have fewer children:
- If you are male, marry an older or less fertile woman.
- If pagan, Zoroastrian, or following the Eastern religions, don't take concubines.
- Imprison your spouse once you have an heir.
- If you feel like you have enough children, there are ways for your character to become less likely to have children. Events can make your character castrated (
), or less fertile (
). There are also societies that at a certain rank allow you to choose to become 
.
Sire bastard children:
- If
Way of Life DLC is activated, select the seduction focus. - Select people with good genetic traits that are close to you.
- Use the "Find Characters" menu to find them.
characters are usually swooned with more success.
- Repeat one-night stands by choosing to "love and leave".
- Wait three months and check if you or your target have been successfully impregnated, if not then seduce them again.
- Do this with as many people as you like.
- Usually three is sufficient.
- Have many children to increase the odds of having babies with good genetic traits.
- Don't forget to actually acknowledge them as your bastard.
- Legitimize the best one.
- This strategy can be used as backup in case your dynasts fail to produce a desirable heir.
- Optional: Choose not to marry in order to avoid "Unfaithful Lecher" -100 opinion maluses with your spouse. Marry after you have selected a heir.
Organizing the division
Titles given out before succession will still be taken into account for the calculation. For instance, giving out duchy titles of some smaller/further duchies to other sons can ensure that your heir will inherit that big center capital duchy in addition to the kingdom.
This is best suited for an aggressive expansion play-style, where conquered lands can be given out without lowering your own demesne.
Don't use the decision to have your chancellor hand out titles; do it yourself instead, even if you have hundreds of surplus titles. This decision has a habit of distributing them to your sons in a way that leaves your primary heir with nothing but your primary title and a single county, making a succession war all but inevitable.
Keeping a single primary title
- This subsection is out of date: some of these situations no longer prevent the land in question from going along with the kingdom grant
Avoid creating additional kingdoms until you are ready to form an empire. (Keep in mind the gold and piety cost, particularly the gold cost as it costs more gold to create the empire title after paying the 200 piety to form the second kingdom.) If you find yourself with a second kingdom, try to "destroy" the extra kingdom by giving it to a count who will receive few duchies with the kingdom because:
- The duchies are not formed
- The duchies are held by you
- The duchies are held as secondary duchies
- The dukes are direct vassals of a king who is your vassal
- The dukes are at war (e.g. with each other, or in a crusade)
Alternatively, ensure your primary kingdom is the strongest, and push your claims against your siblings after succession.
Preventing succession crisis
Because your siblings inherit land and have a claim on your primary title, they are likely to create claimant factions. You (the primary heir) most likely have low prestige, a shrunken demesne, and (especially if you're unreformed pagan) a "short reign" penalty with most or all of your vassals. Between your siblings' power and your lack of power, bloody civil wars are likely.
Some possible strategies:
- Many weak heirs: it may be easier to deal with many weak heirs that may fight against each other, rather than one strong brother that can challenge your power all by himself.
- Strong capital: A primary heir is likely to get the capital county, so researching technology, constructing holdings and buildings can ensure said heir an advantage over their siblings. Due to de jure preference, the primary heir will also likely keep the duchy and even kingdom that contains the capital, if in a kingdom or empire.
- Inheritance of gold: the wealth of a ruler is not divided on gavelkind succession, which can be used by the heir to smooth the transition (bribes, mercenaries, ...)
- Retinues and outlying vassals: Retinues are not divided up but all go to the primary heir; and the only direct vassals your siblings get are the de jure ones. A large multi-duchy kingdom can conquer many duchies outside its de jure borders, and the vassals there will be compelled to send troops to your reunification war. (Just be sure that such vassals are still within the empire which your kingdom belong to de jure.) A large retinue on the border can strike opposing armies before they can organize, if fighting a reunification war is necessary.
- Prepare opinion boosts for your heir to use as soon as he takes the throne.
- Leave some duchies uncreated, so your heir can get prestige and "granted a duchy" opinion bonuses. (This may not be possible if you're close to your vassal limit.)
- Leave some counts as direct vassals, so your heir can transfer them to dukes.
- Keep loot aboard ships for the prestige bonus.
- Consider a mix of counties and baronies within your capital duchy as your demesne: Besides holding onto only one title of each tier (from duchy to empire, if applicable), consider a mix of counties and baronies within your capital duchy (or even capital county) as your demesne. The secondary heirs are more likely to inherit baronies rather than counties, making them much easier to control. The land, being inside your capital duchy, will be useful as well.
Appointing temporary vassals
Grant your extra counties and duchies to men who do not (and will not) have heirs. Their titles will not count as part of your demesne to be divided by gavelkind, but will eventually return to your primary heir—along with any unspent wealth and tech points.
The temporary vassal should be kinless, old, and less fertile: 
, 
, 
, 
, 
, 
, or . Betroth him to an infant girl, making it difficult for him to have children, especially if his religion does not allow polygamy or concubinage. If you are Greek and control your religious head, you could even excommunicate him, and after giving him the title, imprison and castrate 
him.
Combining succession types
If you hold multiple titles for which you can change the succession law, for example an empire and a kingdom, you can set the highest title to gavelkind and all other titles to primogeniture. This grants the benefits of gavelkind succession (+30% demesne, no prestige penalty for unlanded sons) without causing title splits (provided that all titles lower than the rank of king are located within the de jure kingdoms that you set to primogeniture).
The flaw in this method is if you have multiple potential heirs and your firstborn has a similarly eligible child and then dies. Gavelkind gives priority to younger siblings, and primogeniture prioritizes grandchildren of older children, so the empire and kingdoms will split. Using feudal elective instead of primogeniture can work around this issue, especially if you use a small kingdom as your personal demesne.