Sex - Autonomy

Unless disabled in settings, Sims will decide to have sex on their own, either with a partner or alone. Most of the behavior is altered by the Sex Autonomy Level setting.

Sex autonomy can happen from any of these triggers: partner randomness, solo randomness, watching sex, watching porn, romance conversation or joining to existing sex. No matter which one, explained below rules apply.

Autonomy Triggers

Partner random trigger attempts to start sex autonomy once every in-game hour by rolling the base random chance. Each failed attempt increases the chance of the next attempt by half of the base random sex autonomy chance. Base chance is boosted at night by 0.3%-0.5% and on weekends by 1.5%-1.7%. Lots that have the Hypersexual trait increase the base chance to 100%, guaranteeing a successful roll every time. Additionally, the Hypersexual trait triggers the sex autonomy multiple (4-2) times in a row.
Base chances: High Level: 5.6%, Normal Level: 3.5%, Low Level: 3.0%

Solo random trigger attempts to start solo sex autonomy once every half of an in-game hour by picking Sims that have at least 50% of desire or by random Sim base chance. Sim will not be picked if a possible sex partner is around. Afterwards, base chance is rolled to decide if solo sex autonomy will occur.
Sim Base chances: High Level: 20%, Normal Level: 15%, Low Level: 10%
Base chances: High Level: 8%, Normal Level: 5%, Low Level: 3.5%

Watching sex attempts to start solo sex autonomy every 7.5 seconds by picking Sims that are watching active sex. Base chance is boosted by 15% when the watching Sim has the 'Cuckold' trait.
Base chances: High Level: 15%, Normal Level: 10%, Low Level: 5%

Romantic conversation trigger attempts to start sex autonomy after every successful romantic social interaction. Base chance is boosted by 10%-25% when both Sims are flirty and by additional 10%-25% when the partner has very high desire (at least 80%).
Base chances: High Level: 25%, Normal Level: 10%, Low Level: 5%

Joining to sex occurs every 6 seconds when any Sim is in sex. If tested Sim is less than 6 distance units away and the sex interaction didn’t reach its actors limit, Sim will join. Every sex interaction starts with a random actors limit, from 2 to the highest possible number of actors.

Picking Sims

Sims picked for sex autonomy are checked in two ways.

Initially, only Sims that pass requirements are allowed for autonomy. These requirements include age, no critical needs, no fear of pregnancy, not being an event or special Sim, and not being in important situations (like work or wedding).

Then all sex autonomy that involves multiple Sims requires scoring their relationship compatibility. Sims are checked for their family relations, relationship context, relationship levels, skills, traits, moodlets, current situation, and desire. Additionally, NPC Sims check for gender preference and get a boost depending on the autonomy level setting.

Picking Location

Sims pick one of the available sex location styles (public, open, semi-open, comfortable or private) based on the time of the day (if it’s night), the time of the week (if it’s weekend), if there is a party happening, if it’s a residential lot, if it’s the home of the picked for sex Sims, if it’s the same zone as the home of the picked for sex Sims, and if it’s a special lot (like bar, lounge, club, library, museum, arts center, relaxation center, gym or pool). Additionally core elements like accessibility, routability and available animations are checked as well.

A public location style is anything outside the current lot. Sims will pick a public location if they are not allowed on the lot or at night but only on Normal or High Level setting. High Exhibitionism skill level will increase the chance of picking this location type.

An open location style is generally a place that has no roof but is inside of the lot or is a really large room. Sims will pick an open location more often at night and when at home or at a special lot. High Exhibitionism skill level will increase the chance of picking this location type.

A semi-open location style is simply a spacious room of any type. Sims will pick a semi-open location more often on High and Normal Level setting. High Exhibitionism skill level will increase the chance of picking this location type.

A comfortable location style is any room that contains objects considered as comfortable (like couches, beds, tables, and chairs). Sims will pick a comfortable location more often when at home.

A private location style is any small room without people in it or rooms considered as bathrooms. Sims will pick a private location more often when not at home.

With every location style, and depending on the way it was picked, a base chance is paired, which gets rolled, and if it fails, autonomy will not proceed. The base chance can range from 10% to 100%.

Once a location style is picked, all objects and rooms are scored based on the chosen style. Everything that fits the style and is nearby will score higher. One of the highest scored location is then used for sex.