The Morningstar Star Rating is derived from a quantitative method in which mutual funds are ranked on the basis of their historical returns (adjusted for risk and costs) over periods of at least three years. These “risk-adjusted returns” are based on the monthly returns of a fund, where downward variations result in a lower score and a consistently good performance is rewarded with a higher score. Another important aspect is costs, making it more difficult for relatively expensive funds to receive a high star rating.
The top 10% of funds in each category receive five stars, the next 22.5% receive four stars, the next 35% receive three stars, the next 22.5% receive two stars and the bottom 10% receive one star. This Star Rating is calculated over periods of the past three, five and ten years. If possible, Morningstar will also calculate these ratings for all periods in its Overall Morningstar Star Rating.