Graduation rates are calculated based on 4-year, 5-year and 6-year time frames. These are often referred to as 100%, 125% and 150% rates. These are calculated based on intitial freshmen cohorts (entry year) and reported to IPEDS by gender and race. This data is also reported for many surveys. Often a moving average (3 to 5 year) is employed to smooth out fluctuations from unusually high or low rates for a given year.
Often people refer to "adjusted" graduation rates. Adjustments are made to cohorts for death, military service and/or absence for a religious mission. People in these categories are removed from graduation rate calculations.
In August, IPEDS was ordered to begin calculating a "200%" rate, or the rate for graduating within eight (8) years of initial enrollment.