Population

Version

Please help with verifying or updating older sections of this article. At least some were last verified for version 3.9.

This article is for the PC version of Stellaris only.

**Population**, also known as **pops**, is the center of productivity and political action within an empire. They provide resources by working in  jobs created by  districts and  buildings, and also produce  unity if they are part of a specific  faction.

## Demographics

Each planet has three variables that determine its demographic dynamics. At any time a planet can have only one growing pop, one declining pop and one assembling pop, and their speeds determine the demographics.

### Pop growth

 **Pop growth** represents the increase in population from natural reproduction and immigration. Its unit of measurement is *pop per month*. Growth points accumulate every month by adding the month's pop growth, and after reaching a growth progress goal a new pop appears. The growth progress goal is dynamic and depends on the total empire population: growth progress goal = 100 + growth required scaling × total empire population

The growth required scaling value is a game setting. The more pops a empire has the more growth points are needed to be accumulated for the next pop.

Monthly  pop growth is a function of

* the *base pop growth*: a sum 3.0 pop/month and pop growth from pops
* percent bonuses for pop growth
* migration per month
* percent bonuses for pop migration:

# pop growth
(
3.0
pop growth from pops
)
⋅
(
∑
percent bonuses for pop growth
)
migration
⋅
(
∑
percent bonuses for migration
)

{\displaystyle \text{pop growth} = (3.0 + \text{pop growth from pops}) \cdot ( \sum \text{percent bonuses for pop growth}) + \text{migration} \cdot ( \sum \text{percent bonuses for migration}) }

The *base pop growth* is depends on the number of pops on the planet and a logistic curve-like dictated by the  planet capacity value. Then pop growth modifiers are applied. And lastly pop growth from immigration/emigration is added/subtracted with its modifiers.

Base population growth formula:

planet capacity

2

>

planet population

{\displaystyle \frac{{\text{planet capacity}}}{2} > {\text{planet population}}}

# total base growth
3
⋅
max
(
0.125
⋅
(
population
−

population
2

planet capacity

−
1
)
,
1
)

{\displaystyle \text{total base growth} = 3 \cdot \max (0.125 \cdot (\text{population} - \frac{\text{population}^2}{\text{planet capacity}} - 1) , 1)}

planet capacity

2

≤

planet population

{\displaystyle \frac{{\text{planet capacity}}}{2} \le {\text{planet population}}}

# total base growth
3
⋅
0.125
⋅
(
population
−

population
2

planet capacity

−
1
)

{\displaystyle \text{total base growth} = 3 \cdot 0.125 \cdot (\text{population} - \frac{\text{population}^2}{\text{planet capacity}} - 1)}

On the left is a plot of base population growth as a function of the planet's population from 1 to 99 (X axis) and the planet's capacity from 15 to 104 (Y axis). For reference a number of planet capacity values for zero development cases are given in the table:

 21
 29
 62

Base pop growth values spawn between minimum of 0.3 per month (Cyan color) and the maximum value of

(
logistic growth ceiling
⋅
3
)

{\displaystyle (\text{logistic growth ceiling} \cdot 3)}

 growth per month (Gold color on the graph). The logistic growth ceiling game setting determines the maximum base growth. By default:

# logistic growth ceiling
1.5

{\displaystyle \text{logistic growth ceiling} = 1.5}

;

# Max Base pop growth
4.5

{\displaystyle \text{Max Base pop growth} = 4.5}

.

The plot of the base pop growth has the following features:

Species can be chosen manually for growth if the Population Controls policy is set to *Allowed*. Otherwise it is done automatically following in game logic: any species existing on the planet or which has immigration access to the planet may be selected to grow there. When choosing a species to grow, planets will generally prioritize species that are under-represented on the planet and have citizenship equal to that of the already existing species. If immigration access is lost to all planets containing the currently selected species, a new species will be selected and all existing growth progress will be erased.

Pop growth stops when a planet is 15% overcrowded and has 5 pops without housing. Pops start to decline when a planet is 25% overcrowded.  Planet capacity is capped at 500, regardless of free housing or unblocked districts. Pops can go over 500 and will not stop growing (or decline) until the *required housing* exceeds *available housing* by 15% (or 25%).

 Habitability is an important pop growth modifier. Pops on low habitability planets will reproduce slower and migrate. Every **1%** reduction of habitability below **100%** reduces  species growth by **−0.5%**. At **0%** Habitability pops have **−50%** growth speed.

#### Migration

 **Migration** is calculated by subtracting **emigration push** from **immigration pull**, both of which are determined by factors such as  housing,  stability and  unemployment. A planet with more emigration than immigration will have its  growth speed lowered and the amount lowered will be added to potential immigration targets. Planets with higher immigration pull will receive a greater share of this migration, which is converted directly into pop growth. Signing a  migration treaty will allow migration to and from another empire's planets. A newly colonized planet gains **+100** immigration pull and divides a total of **+50** emigration push between all developed planets, until  15 years have passed or the colony has 10  pops.

 **40%** habitability is the minimum that will be considered for automatic migration.

#### Growth weight

The exact mechanics by which a new pop is selected for growing/assembly is not fully known. However a bunch of values can be extracted from the Stellaris/common/defines/00\_defines.txt file.

### Pop assembly

**Pop assembly** represents a planet's capacity for constructing  Mechanical,  Machine, or biological pops. Pop assembly can be either robotic or biological at a given time; both cannot be produced simultaneously. Once

100
(
growth required scaling
⋅

total empire population

)

{\displaystyle 100 + (\text{growth required scaling} \cdot {\text{total empire population}})}

 assembly points are reached, a new pop is created on the planet. Non-sapient robotic pops do not migrate but can create overcrowding and unemployment. The constructed template is the one with the highest number of used trait points, but can always be changed manually; unlike choosing a species to grow, this does not cause a penalty to assembly speed.

 Robotic pop assembly is affected by traits and other modifiers.

 Organic pop assembly is not affected by any traits or modifiers except for the following:

* **+5%** per  Medical Worker Job
* **−25%** from  Lithoid
* **−75%** from  Necrophage

### Pop decline

**Pop decline** represents the decrease of certain species on the planet due to purging or severe overcrowding. A pop will disappear after 100 decline points have been accumulated. By default, decline rate is **−5** decline points per month. Overcrowded planets that have over-represented species will have those species begin to decline in numbers and be replaced by newly growing, under-represented species that have equal citizenship. Purging a particular species will cause that species to decline more rapidly depending on the purge type; the decline factor from purging overrides natural decline factors.

### Resettlement

Resettlement is the process of pops moving from one planet to another, more desirable one.

#### Automatic resettlement

Sapient, unemployed, free pops have a chance each month to automatically resettle to another planet with available jobs and housing and suitable habitability. If a  Slave Processing Facility is active on the planet, enslaved pops and robots in servitude are also eligible. Pops cannot automatically resettle from planets that have been colonized for less than 61 months.

 Migration controls will prevent this (except for sapient robots). Empires that outlaw slavery (and hence the slave processing facility) cannot enable automatic resettlement for robots in servitude.

A  Transit Hub starbase building will increase the monthly chance of a pop automatically resettling.

#### Forced resettlement

If the empire's  Resettlement policy allows it, forced resettlement will instantly move a pop from one planet to another. This costs a base amount of  energy and  unity determined by the pop's stratum, which may be reduced by additional modifiers.

## Happiness

Each pop in an empire has a **happiness** rating. It ranges from 0% to 100% and has a base level of 50%. Happiness determines approval rating when combined with stratum  political power, as well as the following effects:

* Each point of happiness above 50 adds **+1%**  governing ethics attraction to free pops and **+2%**  Authoritarian ethics attraction to slaves.
* Each point of happiness below 50 adds **−1%**  governing ethics attraction to free pops and **+10%**  Egalitarian ethics attraction to slaves.
* Each point of happiness above 50 gives each pop **−0.02**  crime, up to **0** per pop at 100% happiness.
* Each point of Happiness below 50 gives each pop **+0.02**  crime, up to **+2** per pop at 0% happiness.

Fortunately, there are many ways to improve happiness in an empire. Planetary  edicts, civics,  living standards, permanent modifiers,  planet modifiers, and  ruler traits can positively affect happiness.

 Faction approval also plays a major role in pop happiness and Events may have an impact on planetary or empire happiness for a limited time as well.

### Approval rating

Pop approval rating is a measure of the population's support towards the empire. It is determined by the average  happiness of each stratum, weighted by  political power. Pops without happiness are treated as having 50% happiness (for example: pops with  Nerve Stapled trait, pops with  Machine trait). The displayed approval rating is rounded down, as is the displayed  stability bonus.

# Approval Rating

∑

Pop

happiness
⋅
political power

∑

Pop

political power

{\displaystyle \text{Approval Rating} = \frac{ \sum\_{}^\text{Pop} \text{happiness} \cdot \text{political power}}{ \sum\_{}^\text{Pop} \text{political power}}}

Note: Pop drones with the  Rogue Servitor civic act like they have  political power = 0.09 and  Bio-Trophy pops have  political power = 1 (only for the purpose of this formula).

Approval rating ranges from 0% to 100% and has a base level of 50%.

* Each point of approval rating above 50% adds **+0.6**  stability, up to **+30**  stability at 100% approval rating.
* Each point of approval rating below 50% adds **−1**  stability, up to **−50**  stability at 0% approval rating.

## Upkeep

Upkeep of a pop heavily depends on the type of pop and the type of empire. Usually it consists of:

* Base upkeep – some basic resource for the pop to sustain itself
* Living Standards upkeep – an amount of  consumer goods
* Job upkeep – additional resources needed for the pop to perform its job
* Housing needs – a planet wide resource for pops to live in
* Amenities needs – a planet wide resource for pops to be happy about

Colony habitability lower than **100%** for specific pop leads to penalties in the form of increased pop base upkeep and amenities needed for that pop.

*See also: Colonization#Habitability*

### Base upkeep

Base upkeep is always **1** of a  basic resource per month, which depends on the type of pop and possibly its traits. Biological pops consume  food, while  Lithoid pops consume  minerals;  Mechanical pops ( Robot and  Machine) consume  energy. Certain species traits can replace part or all of a biological species' base upkeep with energy as well.
Fungoid or Plantoid pops with the  Phototrophic trait replace half their base upkeep with  energy upkeep. As do pops with the  Radiotrophic trait, with the addition that they require no energy upkeep when living on a  Tomb World.  Voidling replaces all of a pop's base upkeep with  energy upkeep.  Exotic Metabolism adds  **0.125** exotic gases upkeep and  Cyborg traits add additional energy upkeep.

After base upkeep is determined, it can be modified by species, planet, or empire modifiers. For example,  Zombie pops have **−100%** base upkeep. Although there is a hidden cap of **−90%** for the sum of modified applied, this makes base upkeep always non-zero.

Note: *Organic* pops includes Biological and  Lithoid pops.

**Base upkeep**
* **0.5** energy
* **0.5** energy
* **0.5** energy

### Living standards upkeep

*See also: Living standards*

In addition to base upkeep, non-Gestalt pops, including  Bio-Trophies, require a certain amount of  consumer goods based on their living standards. Synthetic ( Mechanical) pops that are given citizen rights require consumer goods as well. The amount of consumer goods typically depends on the pop's stratum, but other modifiers can increase or decrease this amount.

### Housing

**Housing** represents the living space available for pops to live comfortably. Housing is primarily provided by districts, with  city districts giving more housing than their resource-focused alternatives. Each pop requires 1 unit of housing by default but the housing demands of individual pops can change due to a variety of factors. If the number of pops exceeds the amount of housing it will cause  stability to drop by

40
⋅

missing housing
total housing required

{\displaystyle 40 \cdot \frac{\text{missing housing}}{\text{total housing required}}}

 and a flat **+50** planet emigration push.

As a rule of thumb, each resource district exactly pays for itself in terms of housing, while the pops that work building jobs need city districts (or housing buildings) for their housing, though the capital building provides some buffer before cities are needed. This applies equally to  Ecumenopolises. The  Agrarian Idyll civic gives extra housing to resource districts, allowing the empire to house its pops working building jobs mostly via resource districts. The Trans-Stellar Corporations tradition adds jobs to habitat trade districts, but does not match them with additional housing, making some residential districts necessary.

### Amenities

**Amenities** represent the infrastructure and jobs dedicated to fulfilling the needs of the population on a given colony. Individualist empires obtain amenities from a variety of jobs while  Gestalt Consciousness empires obtain them primarily from  Maintenance Drone jobs. High amenities grant increased  happiness to citizen pops in regular empires and increased  stability in  Gestalt Consciousness empires, while insufficient amenities will lower pops' happiness (or stability, for Gestalts) on the colony.

Pops have a base amenity requirement of  **1** Amenities,  slaves require **0.75**, and non-citizen Robots require **0.5**. The shown  amenities value is the *available amenities* value, or the surplus. After base amenities upkeep is determined, it can be modified by species, planet, or empire modifiers. **5** Amenities are always lost on every colony due to inefficiencies. The formula for available amenities (or extra amenities) is the following:

# Available Amenities
Amenities Provided
−
(
5
Pop Amenities Usage
# )

{\displaystyle \text{Available Amenities} = \text{Amenities Provided} - (5 + \text{Pop Amenities Usage}) = }

=
(
Amenities Provided by Buildings
(
Amenities Provided by Jobs
⋅
∑
modifiers with Job scope
)
)
⋅
∑
modifiers with Planet/Empire scope
−

{\displaystyle = (\text{Amenities Provided by Buildings} + (\text{Amenities Provided by Jobs} \cdot \sum \text{modifiers with Job scope})) \cdot \sum \text{modifiers with Planet/Empire scope} - }

−
(
5
Pop base Amenities Upkeep
⋅
∑
upkeep modifiers
)

{\displaystyle - (5 + \text{Pop base Amenities Upkeep} \cdot \sum \text{upkeep modifiers}) }

One impactful upkeep modifier is the effect of subprime habitability on the specific pop.

Most values representing amenities are rounded to the closest integer value (the tie-breaking rule is unknown), except for *amenities from pop jobs* - it is rounded down.

The formula for available amenities or amenities deficit effect on a planet's  happiness ( stability for Gestalt empires) is not strictly linear, with less effect for extra amenities than missing amenities.

The formula for extra amenities (*available amenities* > 0 case) contributing to  happiness is:

# happiness bonus
min

(

20
%
,

20
⋅

⌊
available amenities
⌋

⌊
pop amenities usage
⌋

)

{\displaystyle \text{happiness bonus} = \text{min} \left( 20\%, \frac{20 \cdot \left\lfloor \text{available amenities} \right\rfloor}{\left\lfloor \text{pop amenities usage} \right\rfloor} \right)}

In other words, it scales from **+0%** with 0 available amenities, to **+20%** with twice as many available amenities as necessary.

The formula for a amenities deficit (*available amenities* < 0 case) affecting  happiness is:

# happiness penalty
max

(

−
50
%
,

200

/

3
⋅

⌊
available amenities
⌋

⌊
pop amenities usage
⌋

)

{\displaystyle \text{happiness penalty} = \text{max} \left( -50\%, \frac{200/3 \cdot \left\lfloor \text{available amenities} \right\rfloor}{\left\lfloor \text{pop amenities usage} \right\rfloor} \right)}

In other words, it scales from **+0%** with 0 available amenities, to **−50%** when the planet has less than 25% of amenities needed.

Note: for readability reasons in the formulas above for the happiness effect as a function of amenities the rounding operations are noted as *rounding down* when in reality *rounding to the nearest integer* is used.
The  stability bonus or penalty received by  Gestalt Consciousness empires from amenities in a colony by value is the same %-value a non-Gestalt empire gets in  happiness (the formulas above can be used).

Amenities can be affected on an empire-wide basis by the following:

## Stratum

Strata represent pops' social classes. The higher a pop's stratum, the more political power they have and the more  consumer goods they require for upkeep, according to their living standard. It also determines the resettlement cost. Resettlement costs no  unity if the empire has the  Corvée System,  Subsumed Will, or  OTA Updates civic, or if the pop is enslaved or a non-sentient robot.

If a pop takes a job above its stratum, it will be promoted to the higher stratum. If there are no available jobs of equal or higher stratum the pop will become unemployed, slowly demoting in stratum and causing  happiness penalties in most living standards. The  Shared Burdens civic and living standards each reduce demotion time by **−45%**, the  Kinship tradition reduces it by **−75%**, and being in default reduces it by **−50%**.  Slaves demote instantly, regardless of stratum.

## Slavery

Entire species can be enslaved by giving them a certain citizenship, which opens a new tab in the Species Rights menu called *Slavery Type* that determines what are the effects of slavery.

 Any

Enslaved pops also use only  **0.75** amenities and  **0.75** housing (instead of 1), which can be further reduced if the  slavery type is Servitude or Livestock. They also have a  resettlement cost of just  50 energy. Enslaved pops cannot join factions and have only  **25%** political power, or **18.7%** if a Slave Processing Facility is present on the planet. However, they can still increase  crime if they're too unhappy.

Low  stability is more dangerous when enslaved pops are present on a planet. Normally dangerous events can only occur if it's lower than **25**, but if any pop is enslaved it should be kept above **40**.

### Slaves, workers and specialists

In addition to the slave resource output modifiers, worker resource output modifiers can also affect slaves in worker jobs. As of 3.0.1, slaves in specialist jobs are affected by specialist output modifiers, but not by slave resource output modifiers, if in Indentured Servitude.

* Slaves working on  miner jobs can benefit from  worker resource output modifiers, such as  Authoritarian and  Strong.

If a modifier affects the resource output of both workers and slaves, it actually affects slaves in worker jobs twice.

* The  Extended Shifts edict increases slaves resource output by **+10%** and workers resource output by **+10%**, resulting in an total **+20%** bonus to slaves in worker jobs.

Modifiers that affect workers aside from the resource output ones don't affect slaves.

* The  Extended Shifts edict decreases slaves' happiness by **−10%** and worker happiness by **−10%**. It does *not* cause the slaves to suffer **−20%** happiness.

## Ethics attraction modifiers

**Ethics divergence** is where a pop or group of pops decide to follow a different ethic than the general population. A materialist pop may decide to follow a more spiritual path and a pacifist culture might decide that peace is the path of the weak.

Each pop in an empire will only embrace a single, non-fanatic ethic. At the start of the game, the population will be made of the empire's governing ethics. As population expands and eventually is divided over various planets and sectors, certain segments may decide to adopt values that are different from the core values of the species due to various circumstances in and around the empire.

Each ethic has a certain attraction value attached for all pops, depending on both the empire's situation and their own. Each pop can only switch ethics once per year. The exact values and options that influence the attraction levels of certain ethics can be found at Ethics attraction. The attraction factors of ethics can be amplified by certain circumstances such as policies or traits.

Having a positive ethics attraction effect will let all actions that increase attraction to the government ethics result in even more attraction, and negative amounts will be decreased. With a modifier of **50%**, an action that would increase attraction by 2 would instead increase by 3.

Hovering over a pop's ethic will display the attraction towards all ethics.

## Robots

**Robots** are artificial pops and can be constructed once the required technology becomes available. They have the  Mechanical trait, giving them  **+200%** habitability on any planet. Robots can be given new traits via robo-modding, and the species template with the highest number of used trait points will be built by default. A different template can be specified for each planet.

The jobs a robot can have are limited by the highest robot technology researched. If an empire researches the  Synthetics technology with AI policy set to *Servitude* or *Citizen Rights*, all robots immediately become sapient, gain ethics, are affected by empire and planetary  happiness modifiers and contribute to crime. With *Citizen Rights* they also become affected by all  happiness modifiers.

* Specialist if AI policy is set to *Servitude*
* Specialist (except  Researcher,  Bureaucrat and  Culture Worker) if AI policy is set to *Outlawed*
* if AI policy is set to *Servitude* or *Citizen Rights*

Robots without *Citizen Rights* require 50% less  housing and  amenities and do not need  consumer goods. If a planet with sapient robots is captured by an empire that doesn't have the  Synthetics technology, they lose their sapience, and if a planet with non-sapient robots is captured by an empire that has the  Synthetics technology and does not have the *Outlawed* Artificial Intelligence policy, they are immediately given sapience. Note that non-sapient robots can do all specialist jobs with  Droids tech, but not after researching  Synthetics tech.

* It's possible to take the  Synthetic Evolution ascension perk and turn all organic pops and leaders into synthetics.
* Hive Mind empires cannot build robots and will always purge all robots on their worlds.

* As long as an empire has the Artificial Intelligence policy set to *Servitude* there is a risk of them starting an AI rebellion, if either the *Synthetics* or *Sapient Combat Simulations* techs have been researched.
* Machine Intelligence empires cannot build robots, but they can use them as drones if conquered from a regular empire or bought on the slave market. Robots in a Machine Intelligence empire can work all jobs and are not affected by happiness.

## Purges

**Purges** represent the systematic elimination of specific pops or entire species from an empire and can be done on a per pop or species basis.

Targeted pop purging still requires applying the species-wide  slavery at minimum and it is limited to a basic extermination, although without production penalty.  Gestalt Consciousness empires can purge their pops of any composition freely, with exception of  Bio-Trophies.

Species-wide purging is done by setting the species'  citizenship to  Undesirables.  Gestalt Consciousness pops in empires of different authority are forced to be set as Undesirables, unless they can be assimilated. Therefore, gaining planets from a Gestalt Consciousness empire means that the planet will be lost when it is empty of the conquered pops if there is not at least one non-gestalt pop on it. There are also four special cases:

* Pre-sapients can only be purged if the  Pre-Sapients policy is not set to Protected and they are automatically purged if it's set to Extermination.
* Robots are automatically purged if the  Robotic Workers policy is set to Outlawed.
* Synthetics can only be purged if the  Artificial Intelligence policy is not set to Citizen Rights.
* Empires with the  Evolutionary Mastery ascension perk can change the citizenship of hive mind pops to  Assimilation, which prevents them from being purged.

Fallen and Awakened Empires can choose not to purge Hive-Minded/Machine pops.

Having any species-wide purge is a negative issue for Xenophile factions, aside from the case of  Gestalt Consciousness pops and outlawed robots.

There are multiple types of purge available, determined by the  Purge Type species rights.

## Refugees

Pops from other empires may flee to escape purges, slavery, resettlement, crisis bombardment, or as a result of land appropriation. Whether another empire is willing to accept those fleeing depends on its Refugees policy. Refugees will not head for empires where they have the *Undesirables* citizenship. Accepted refugee pops will get  **+20** happiness for 10 years.

Once refugees are generated they will head for any empire that will accept them with their *Refugees* policy following the following order:

1. Habitability at least 70% and  housing at least 1
2. Habitability at least 70%
3. Habitability at least 50% and  housing at least 1
4. Habitability at least 50%
5. Habitability at least 20% and  housing at least 1
6. Habitability at least 20%
7. Housing at least 1
8. Any other planet

Pops that are  robotic or have the  Hive-Minded,  Nerve Stapled or  Zombie traits cannot become refugees.

## References

1. ↑ from the patch 3.7 notes: Capped resource upkeep/cost/production reduction modifiers to -90% for any given case. I.e. you will no longer be able to have completely free upkeep on jobs which are meant to cost upkeep.
2. ↑ The effects are set in 00\_static\_modifiers.txt at `planet_amenities_high`, `planet_amenities_low`, `planet_amenities_no_happiness_high`, and `planet_amenities_no_happiness_low`; the threshold for maximum effect is set in 00\_defines.txt at `MAX_PLANET_AMENITIES` and `MIN_PLANET_AMENITIES`.

**Game concepts**