For the prosperity rating, each house is assigned a certain amount of points, depending on its level. Then, all points are added up and divided by the total number of homes in your city. The rating is then rounded to the nearest whole number. This rating is the maximum prosperity rating that can be attained. Another factor that affects the prosperity rating is the amount of money in your treasury: if you're in debt, your rating will plummet to zero.
The prosperity rating is re-calculated once every week, which is four times per month. If the rating is not a whole number, it is rounded to the nearest number.
Imagine your city consists of:
- 25 medium insulae
- 10 small domus
- 5 large estates
The total number of prosperity points:
- Insulae: 25 x 10 = 250
- Domus: 10 x 1 = 10
- Large Estates: 5 x 220 = 1100
- Total: 250 + 10 + 1100 = 1360
The total number of houses in the city is: 25 + 10 + 5 = 40.
The prosperity rating is then: 1360 / 40 = 34.
To help you calculate the prosperity rating of your city, we've created a prosperity calculator.
Increasing prosperity rating
Increasing your prosperity rating can basically be done in two ways:
- Decreasing the number of low-level houses
- Increasing the number of high-level houses
Eliminating low-level housing: if you have many small insulae, small domus or small villas in your city, which all have only one point, your rating will be low. Evolving those to the next level will usually increase your rating considerably. In the example above, evolving the small domus to medium domus will increase your prosperity rating to 40.
Another way to increase your prosperity rating is to increase the number of high-level houses. This can be done in two ways: by upgrading the houses you already have, or by building more (patrician) housing of the same level as you already have. In some scenarios, the patrician housing level is limited by the number of exotic goods you can import (or sometimes the culture buildings available), so in that case, the only thing you can do is build more patrician houses of the maximum attainable level.