What is the formula for calculating the retention ratio?

Retention rate is calculated by:

Subtracting the dividends distributed during the period from the net income and dividing the difference by the net income for the year.

A good rate is highly variable by industry, there is no set standard for it. A 100% retention rate is good, while a 15% retention rate is generally bad. A good rate is as high as you can get it to go.