Depreciation

Depreciation is a mathematical term for the game mechanic that affects objects purchased in The Sims series. Objects purchased through buy mode, and certain architectural elements purchased in build mode, depreciate and lose value over time. An object purchased for a certain amount will depreciate based on a formula determined for the object, until it eventually reaches a minimum value. Different games in the series calculate depreciation differently, and some have different models for different types of objects.

The Sims
In The Sims, an object depreciates at midnight the night after the object is purchased. Objects depreciate on the first day by a certain percentage based on the type of object:
 * Electronics - 25% depreciation on first day
 * Plumbing fixtures and appliances - 20% depreciation on first day
 * Furniture - 15% depreciation on first day

After the first day, items depreciate at a rate of approximately §1 per §100 of the item's original worth, rounded to the nearest hundred. For example, an item originally worth §1000 will depreciate around §10 a day after the first day's depreciation, while an object worth §300 will depreciate by §3 each day.

The Sims 2
In The Sims 2, items depreciate at midnight the night after the object is purchased. Objects depreciate by 15% each day, and do not incur a first-day depreciation penalty. Non-broken objects have a maximum depreciation of 60%, with 40% of the original value remaining. Thus most objects that depreciate will reach their final minimum value on the fourth day after purchase and will not decrease in value beyond that point. Objects which are in need of repair are valued at half of what they would otherwise be worth for their age.

Some objects, such as computers, incur an initial deprecation as soon as they are used for the first time, even if a full day has not yet elapsed. Depreciation beyond this point is based on the initial depreciation price, not the original price of the object. For example, computers in The Sims 2 experience a 10% depreciation the moment they are used for the first time, and will drop 15% each day thereafter from the initially depreciated price. Thus a computer that originally cost §1000 will depreciate to §900 at first use, and will lose 15% of §900 (in this example, §165 a day) thereafter until it reaches the 60% maximum depreciation.

Depreciation does not affect objects in a Sim's inventory.

The Sims 3
Objects in The Sims 3 depreciate immediately by 15% after the player exits Buy Mode, and depreciates by ten percent each day thereafter, stopping when the item reaches 60% of its original value. Objects that are broken or damaged by fire are worth less than they otherwise would be.

The Sims 4
Most objects in The Sims 4 depreciate by 20% once a sim has interacted with it.

Appreciation
Some objects do not undergo regular deprecation, and can even appreciate (i.e., gain value) over time. This notably occurs with paintings, sculptures and other decorative objects. Some architectural elements in The Sims can appreciate over time.