Sentencing Law In Practice

Sentences for crimes vary considerably from state to state. Furthermore, the relationship between the official length of a sentence for a crime and the actual time served varies greatly from state to state. 

• Actual time served in prison is often quite different from the sentence length pronounced in court, and therefore sentence length alone only partially explains the individual and policy-level implications of long sentences.
• The relationship between sentence length and time served varies greatly across states and jurisdictions due to the difference in the legal and statutory framework that governs prison release.
• States that have higher than average sentence length also have higher than average time served, but the relationship between these two factors is modest.
• The average judicial maximum sentence in states with highly indeterminate systems (7 years) is twice as long as in highly determinate states (3.5 years). However, the difference in average time served in highly indeterminate and highly determinate states is much narrower, ranging between 2.1 and 2.6 years.
• Some states are much more likely to impose long prison sentences than others. The proportion of people entering prison with long sentences ranges from 2% in Colorado to 66% in Michigan.
• Individuals serving long sentences in states with highly determinate systems spend, on average, nearly three times as long in prison as individuals serving long sentences in states with highly indeterminate systems.
• Nationally, back-end factors such as the allocation of sentence credit discounts, and for paroling states, the parole release framework explain more of the variation (60%) of average time served than variation in average sentence length (40%).
• States with identical average sentence length can have different average time served based on the degree of indeterminacy and back-end factors. For example, Oregon and Texas both had an average sentence length of 4.4 years in 2016, yet the average time served in Texas (2.1 years), a state with a high degree of indeterminacy, was lower than in Oregon (3.5 years), a state with a low degree of indeterminacy.

From here.