More people are spending time in NSW jails before being sentenced due to increased policing of domestic violence, sex and weapons offences.
However, non-custodial alternatives have reduced the number of prisoners doing time after having terms imposed, based on data from the Bureau of Crime Statistics and Research (BOCSAR).
Released on Thursday, it shows the number of people on remand in the state's jails reached 5055 in December 2023, the highest on record.
Those on remand make up 42 per cent of adults in prison, up from 34 per cent in 2019.
Domestic violence assaults were up by 201 in December compared with 2019, an increase of more than 33 per cent.
"Police are increasingly inclined to charge for those offences," BOCSAR executive director Jackie Fitzgerald told AAP.
"There actually are more domestic assaults coming to police attention and we are seeing more of those translate into legal action."
The number of people on remand for sex offences was up 144 for the same period while those on remand for weapons offences increased by 50, the largest proportional increase at 46.3 per cent.
The amount of people and the time they spent on remand was steady at about 90 days, but a rise in charges increased the population, Ms Fitzgerald said.
However, changes to sentencing options in NSW, allowing people to serve their sentence in the community, drove a 22 per cent fall in the number of sentenced prisoners doing their time in custody.
"That was a conscious decision with regards to what kind of sentencing paradigm is more likely to be beneficial in terms of re-offending, and that has resulted in a decrease in prison sentences," Ms Fitzgerald said.
The 12,091 adults in custody in December was 1544 fewer than in 2019.
There were 174 youths in custody compared to 170 at the end of 2022.
Another change in 2022 meant people convicted of an offence that was likely to result in imprisonment should not receive bail before sentence unless they show special or exceptional circumstances.
Ms Fitzgerald said bail decisions warranted scrutiny.
"It is definitely a change in the administration of justice in NSW ... a lot of people are not at liberty because of those bail decisions, more than ever before," she said.
Prisoners on remand who have been denied release by police or a magistrate can seek bail in the NSW Supreme Court.
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