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Bio Pop Growth
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0.462 MB
Jul 26 @ 2:25pm
Aug 10 @ 12:17pm
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Bio Pop Growth


Adds two new planetary decisions and a corresponding edict that can be accessed from the start of the game. The first decision, Distribute Surplus, adds a modifier to the planet that improves pop happiness, planet stability, and pop growth at the cost of increased food consumption. The pop growth modifier is determined from the planet's current biological pop size and its free housing, which results in logistic pop growth. Each decision has a corresponding edict that applies the decision to each colonized planet and to new colonies. The second decision, STOP Distributing Surplus, removes the modifier(s) added by Distribute Surplus, including the increased food consumption rate. Toggling off the edict applies the STOP Distributing Surplus decision to each colonized planet and prevents the Distribute Surplus modifier from being applied to new colonies.

Distribute Surplus

The Distribute Surplus decision applies a logistic growth modifier to the planet's bio pop growth and its growth from immigration. By default, Stellaris uses linear growth, which means that bio pop growth does not increase as the bio pop size does. Applying a logistic growth modifier can correct this to match more realistic population growth as well as provide a useful mechanic to trade food for growth.

The formula for logistic growth is dN/dt = r * N * (K - N) / K, where dN/dt is the logistic growth modifier, r=3 (which is mapped to 0.03), N is the bio_pops size calculated by Planetary Census, and K is the planet's carrying capacity. A planet's carrying capacity is K = ( (bio_pops) * 1.1 + (free_housing) * 2.4). Free housing is the planet's currently available housing. The coefficients, 1.1 and 2.4, are the overcrowding modifiers. They determine the homeless population that the planet can support. By including an overgrowth modifier, a planet can grow a larger population than it can support, which triggers the games diverse mechanics to handle overcrowding. The final result is a population size that overshoots its housing capacity and then declines as a result. The overshoot and decline model is a more realistic model of population growth and interplays with Stellaris's existing mechanics rather well.

While the Distribute Surplus decision costs nothing, it increases the food consumption of organic species by 300% (minerals for Lithoids).

The effect of this decision is removed by enacting the STOP Distributing Surplus decision, updated at the end of the month. Distribute Surplus can be applied to all colonized planets and new colonies by enacting the Distribute Surplus edict, found on the edicts page. Individual planets can opt-out of the edict by enacting the STOP Distributing Surplus decision. Similarly, the Distribute Surplus modifiers can be removed from all colonized planets and new colonies by turning off the edict.


The current biological pop size and free housing are recomputed every month (for all planets) and each time that the Distribute Surplus decision is enacted (for that planet).

To get the most out of each Distribute Surplus decision, a planet should have 1 free housing for every 3 bio pop. For example, a planet with 15 bio pop should ideally have 5 free housing. Any additional free housing increases the resulting logistic growth modifier and any less free housing decreases the logistic growth modifier. We recommend enacting the Distribute Surplus decision when 1 addition pop is needed to unlock the next building.

Neither the Distribute Surplus decision nor the edict can be enacted if there is a food or mineral shortage. If a shortage occurs, the Distribute Surplus modifier is removed from all colonized planets and new colonies.


This mod only adds new files and does not alter any vanilla values or files. It should be compatible with all other mods. The mod order may need to be adjusted so that UI mods can incorporate the new decisions into the UI. Note that the Distribute Surplus decision is not visible unless the Planetary Census modifier has been applied to the planet from the Planetary Census decision.

While this mod should be compatible with other growth mods, such as stararchitec's Carrying Capacity, using this mod in combination with other growth mods can result in unintended consequences. No DLC required.

Future Work

While balancing is needed, there is currently no additional work intended for this mod. We are bouncing around ideas for growth that can be applied Machines. However, we have not yet identified an idea that we feel is in the spirit of this species types.
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Champ_ian_  [author] Aug 10 @ 12:24pm 
Update pushed:

Patches: Distribute Surplus food consumption to 275% from 250%. This provides a more fair balance for Agrarian/Agrarian Idyll starts.

Patches: Distribute Surplus carrying capacity calculation now uses 1.1 for each bio pop and 2.4 for each point of free housing rather than 1.5 in both categories. This means that free housing provides significantly more weight towards calculating a planet's logistic growth when Distribute Surplus is enacted. This is especially useful for colonies, since districts can boost pop growth by both increasing free housing and open jobs (both increase immigration pull and immigration growth is also logistic when Distribute Surplus is enacted). It also means that planets with a large number of pops need to maintain free housing rates to maximize logistic growth.
Doomwarrior Aug 8 @ 2:28pm 
If you get rid of 3.0 base growth entirely and base growth on existing pops per planet alone you get rid of most issues. One of them being planet count > good planets in terms of growth. Which means just that whatever you build or research its always better to just have one more planet instead. Because 3.0 more growth. As for robots, if you lower the pop production per worker but allow more buildings the robots have to chose if they wanna grow or do something else.
Champ_ian_  [author] Aug 8 @ 10:36am 
Thanks for the feedback @Doomwarrior. We're currently have the 3.0 base growth but we are looking into allowing players to pick a higher starting growth rate.

As for not replacing it, this mod is not intended as a game overhaul. It's intended to provide new strategies for empires that primarily benefit from food production. stararchitec's Carrying Capacity already provides a pop growth overhaul for those that just want to ditch the default growth model.

We have been considering ideas on how to "overclock" assembly rates. Robot assembly is just already so strong that most approaches become oppressively dominant.

Specializing planets towards growth is a very interesting idea. Other mods and origins do currently provide planetary modifiers that increase growth rate and assembly rates.
Doomwarrior Aug 7 @ 1:08pm 
Just out of curiosity why going the way of decsissions and edicts instead of rewriting the entire pop growth model of vanilla. 3.0 base growth is so unrealistic it hurts. A new colony will not have the body count to support a 3.0 growth a bigger colony can easily outperform this but both a forced into this nonsensical linear model, which results in planet spamming and tall empire being significantly worse of in terms of pop growth. Hence why i am curious why you did not apply your model as a replacement.

In terms of robots, i´d say sort of the same logic applies only the production capacity (buildings) limit the growth. So if you build more robot construction buildings your pop growth increases but you sacrifice slots. You could however focus your growth on one planet possibly adding bonusses to the constructing and then resettle / emigrate surplus robots?
Champ_ian_  [author] Aug 3 @ 9:53pm 
Update pushed:

Patches: Distribute Surplus food consumption moved to 250% from 300%.
Champ_ian_  [author] Jul 30 @ 7:22pm 
Update sent out today.

Patches: Distribute Surplus so that it can be enacted on habitats.

Revises: Distribute Surplus so that it is tied to Population Control and Purge policies. Population Control Allowed and Purge Allowed now disables Distribute Surplus and removes all existing Distribute Surplus modifiers from all planets.

Adds: Icon support for Distribute Surplus. The icons are from the megacorp update. I've disabled DLC and they still work. If anyone has issues seeing the new icons because they don't have the DLC, then let me know.
Champ_ian_  [author] Jul 30 @ 6:30pm 
Hey @K. Constantine! I actually have habitable structures turned off for the mod. I'll be allowing habitable structures in the next update.

As far as I can tell, it runs well with Void Dwellers. The low starting pop size does mean a smaller growth modifier compared to a single world start with 30 pops. However, the advantage is that food consumption isn't as high when applied to only a single station.

A working strategy is to designate one station for pop growth. Get free housing to around 2x pop size (build 2 habitation districts) and then apply Distribute Surplus to that habitat. The resulting modifier will be around 25% growth per month but the food consumption can be sustained without negative food income. Once food surplus has reached around 400-500, apply the decision to a second habitat for another 22.5% growth, which can be maintained for about a year.

Note: The growth modifiers on both stations will only increase as you develop new pops.
K. Constantine Jul 30 @ 4:47am 
How are Void Dwellers handled in this mod? Carrying Capacity ruins them pretty much.
Champ_ian_  [author] Jul 28 @ 4:45am 
Best update yet.

Removes: STOP Distributing Surplus edict. Was able to get the toggle on a single edict to work.

Patches: Distribute Surplus edict to be a toggle. When toggled on, this edict applies the Distribute Surplus modifier to all planets and to new colonies. When toggled off, the Distribute Surplus modifier is removed from all planets and is not applied to new colonies. A low-cost check is performed each day to determine if the edict has been toggled off.

Patches: Distribute Surplus modifier to be updated monthly instead of yearly.

Patches: Distribute Surplus edict and decision to be disabled if there is a food or mineral shortage. The Distribute Surplus modifier is also removed from all planets and is not applied to new colonies. Checked monthly.
Champ_ian_  [author] Jul 27 @ 6:03pm 
Added better intelligence to the AI, so they can use the new decisions/edicts without starving themselves to death.