For more details see: data source and enrichment methodology; data spreadsheet .
In the graph above, a significant number of new starts are counted as having served zero months. As noted, this can occur where offenders have a deferred sentence commencement and are then "released" by the Parole Board to serve the sentence on home detention, or (perhaps more commonly) where remand time credited against the subsequently imposed sentence exceeds the required maximum time to serve.
Clearly the majority of offenders serving prison sentences spend relatively short periods of time (less than six months) in prison as sentenced prisoners. Less than five percent of those released each year have spent more than three years in prison.