How much financial support do libraries derive from overdue fines?
At the library where I worked, our allocated budget took the fines into account and subtracted the total amount received in fines from the money the library was given each year. (We did have one blissful year when fines were first introduced and this didn’t happen, and the fine money went to the acquisitions budget.) But even if that had kept up, we’d have preferred to just have the books back on time. Fines tend to be designed to encourage that, rather than financially penalise the patrons to the library’s advantage – that’s why fines tend to be small and capped at a set amount per overdue item.
It probably varies from town to town, but in my town the overdue fines go to the general fund, so they only benefit the library in even smaller ways than if they got to keep them. That said, unless the item is popular and likely to be missed, I also view overdue fines as merely a small extra donation to the town. In Summary: giving to the Friends of the Library is a more helpful way of giving, but being lax and paying the fine isn’t a big deal, either.