Invest

In order to invest in a region your family must have more than 2000 gold of family wealth. Investing causes the region's production to rise dramatically, which causes the region to produce more gold and food. This is what your advisor is referring to when he tells you the expected return on investment, and it's distributed according to the realm and region's normal tax distribution scheme. Your family will not directly receive anything from their investment, although you personally might if you are the lord or a knight of the region. The cost of the investment will vary depending on the amount of gold produced by the region. Investing in a wealthy city may cost over 600 gold, while investing in a poor rural or badlands region may cost as little as 190 gold, or even lower.

Note: Food production in a region can never exceed 100%. When the regional statistics show production over 100%, it only refers to gold production. Food production is capped at 100%.

There are several reasons for which you might want to invest in a region:

Increase food production in the region. This is quite possibly the most common reason to invest in a region. Rural regions that produce large amounts of food commonly also have low gold production, and are thus inexpensive investments. The corresponding increase in production is often quite large. This can be used to temporarily boost the food production of a region that currently has a production level less than 100%. Remember that food production level is capped at 100%, so the increased harvest of a region that is already at 90% will be minimal.
Increase gold production in the region. You can invest in a high gold producing region to increase production to funnel more gold to the knights of the region or the realm as a whole. This is useful when a large portion of your knights will need to refit at the same time, such as when you are anticipating large battles.
Restore production to normal levels. An investment is a quick way to restore production in the region following a monster/undead attack or an enemy looting run. Just be careful the enemy doesn't come back! A few incidents of looting could easily waste your invested gold.
Fame. Some nobles will invest in a region simply to gain recognition for their family, or to display their wealth.

If the investment in the region raises production above the 100% production level, then it will decrease back to 100% over the next several days. The rate of decrease will be greater the higher it is above 100%. If the region's maximum sustainable production is below 100% due to lowered population, then productions levels will drop to that lower percentage. On the other hand, if production is currently below the maximum level sustainable by the population (due to looting, monster attacks, poor maintenance, etc.) then an investment is a quick way to restore production back to the maximum supportable level. Production will not drop back to the original, pre-investment level, it will only drop back to the supportable level. Production will adjust itself as normal from that point. See Investing Examples for some examples of how this works.

A negative effect of investing in a region is the drop in region control. An investment will typical result in a drop of control by one level. For example: from Core to Main, or from Main to Province. For this reason it is quite common for the investing noble to immediately perform normal police work, or hold a harsh court to restore region control.

If the region population is far below the normal level, you will not be able to perform an investment at all. If this is the case, you will have no choice but to wait for the population level to rise before you will be able to invest.

You will receive one Fame point the first time your family makes an investment.