Thirty hours will be lost from the libraries' opening schedules, which is expected to save about $50,000 this financial year and $100,000 next year, largely from staff penalty rates and casual hours.

Libraries in Belconnen, Civic, Erindale, Kingston, Kippax and Tuggeranong, which all now stay open until 8pm one evening a week, will begin shutting their doors at 5.30pm each weekday.

All libraries in the territory will close at 4pm on Saturdays, rather than at 5.30pm.

Libraries ACT director Vanessa Little said the early closing hours would save public money and allow resources to be redistributed to popular library programs.

"We weren't given a target or anything like that, we're always being asked to make sure we're making best use of public money," she said.

Ms Little said up to 100 children were attending some daytime Giggle and Wiggle sessions for toddlers, while some quieter libraries were seeing very few visitors during the evening.

At Gungahlin, one of the busiest libraries, about 250 items were being borrowed during open evenings, whereas at Civic Library 74 items were borrowed on average.

''We divide that by the number of items people took, so people would definitely take more than one, and probably five plus items, so you're not staying open for very many people,'' she said.

''Giggle and Wiggle is especially large, so the more hands we have on deck for those the better.''

Ms Little said no permanent staff would lose their jobs and casual staff members already working for ACT Libraries would continue to do so, although they may lose some hours of work.

Ms Little said she was confident ACT Libraries would still manage to meet its accountability indicators, outlined in this year's ACT budget, of increasing library visits and items borrowed per capita.

"What happens with those loans, they'll move to another day or time or place," she said.

Ms Little said that in the year 2011-12, the ACT was the only state or territory where visits to libraries and loans had significantly increased.

Woden Library will remain open on Monday nights until 8pm, Gungahlin Library on Wednesday nights and Dickson Library on Friday nights.