Like a lot of people, I've been curious about exactly how chemistry works. Since the chemistry system isn't in the normal objects package, it's not something modders can look at. That means that the only way to test it is through empirical tests.

Recently, with the help of SimSpy I conducted a series of tests to see how different characteristics affected chemistry.

I created 7 sims, all female and all set with bisexual gender preferences so they would show chemistry. I made them all the same except for the aspect I was testing. For example, when testing aspiration I made them all the same zodiac and personality.

It was obvious from the numbers that some rounding was happening and that the actual changes were multiples of 1.5. I've figured out what the actual values were but that means the numbers I'm showing will be slightly different than the integers reported by SimSpy. The game chops off the decimal in each category (aspiration, zodiac, etc.) separately before adding them all up so +17.5 from aspiration and +17.5 from zodiac becomes +34 when totalled.

Chemistry is averaged and those averages are reported here. It really doesn't matter if sim A has a turn on that increases attraction by +35 and sim B has +0 for no turn ons; the game reports the average of +17.5 for both.

Obviously the numbers I obtained are useful only if they can be translated to bolts. I didn't prove the exact value of a bolt but I'm fairly certain it is 35 so most things (except personality and turn offs) are in multiples of a half-bolt.

Note that I call the Fortune aspiration Wealth since I abbrevate aspirations to one letter in my own notes (Pleasure is Z).

With that, let's look at how each factor affects chemistry.