Why do prisoners get released before the end of their sentence?

How prison sentences work in the UK

Well, we also wondered the same things and looked into what makes a prison sentence shorter than others.

To start with, not all sentences are treated the same, as some are treated with greater consequences than others.

Legislation allows prisoners with standard sentences to leave partway through their term.

This allows them to serve the remainder of their sentence in community service hours, referred to as leaving on “licence”.

If offenders breach their license conditions, they are called back to prison.

This typically occurs if the convict is found committing a crime or failing to keep in touch with their parole officer.

When serving their sentence, prisoners can be released if the Parole Board has changed over the years.

Most recently, the Sentencing Act of 2026, due to take effect on 1 October, will allow changes for automatic release dates for inmates serving standard sentences.

The most common prison sentences in the UK are standard determinate sentences (SDS), which have a fixed term length.

The forthcoming Sentencing Act will allow prisoners with SDS to be released after serving one third of their sentences.

Compared to the current legislation, prisoners are allowed to leave at the 40% (SDS40) mark of their sentences, but more times than often will go over the halfway point. 

Now you might think to yourself that this does not make sense, but there is some thought to it.

SDS sentences are calculated so that prisoners serve a longer period in case they breach their probation license, so leaving earlier is all within their rights. 

The upcoming Sentencing Act of 2026 will not affect prisoners with extended determinate sentences (EDS) or life sentences.

However there are exceptions, like the SDS40 sentences, the Sentencing Act of 2026 will refrain prisoners convicted of sexual offences against an adult or child to be released earlier than the 50% mark of their term.