Our hours accrue and dump into their bank every pay period, it is not use it or lose it at the end of the calendar year their balances just roll forward, but we do have a cap, that cap is their annual accrual + 80 hours.  If they are bumping up against that max it is their responsibility to get their bank down by taking time off or taking a pay out. 

The last company I worked for had it set up to have an accrual by pay period and it rolled over from year to year if unused. The maximum accrual rate was three times their current accrual level, so as a new employee accruing 3 weeks of paid time off they would cap at 9 if they didn't take any time off. Where I am now they add in the hours to our bank quarterly or something & once we reach our accrual level we stop accruing until the bank drops back down. Its worth noting that my previous employer was about 1500 employees and the one I'm at now is more like 300. 

We have a 'use-it or lose-it plan. Our associates receive PTO based on their years of service ranging from 0-4 years = 18 days, 5-9 years = 21 days, 10-19 = 26 days, and 20+ years = 30 days.

I don't know how ours was originally set but our max accrual is 1040 hours. It used to be 2080 hours!! There is no use it or lose it rule for ours. I think that kind of goes against what PTO is about but maybe others have it. There is no rollover as they just keep accruing to the maximum amount. Employees can cash out PTO anytime they want, it just has to be in 8 hour increments. We also encourage them to have at least 40 left in their bank in case an  STD waiting period would arise. Employees can also donate PTO to other employees if they want to.

I have used the the accrue to maximum # of hours it was equal to the max one could earn in the company - 240hours.