There is not one set amount of money that every ATM holds at a given time. However, most ATMs have the capacity to hold up to $200,000 at one time. Most do not have this much in cash inside of the actual machine, with $10,000 being a more reasonable figure.
In non-peak hours, some ATMs may actually have less than $10,000. This can be attributed partially to a rise in ATM thefts via the smash-and-grab method. ATMs can be serviced during the day by ATM technicians, who insert additional cash once customers make large enough transactions to warrant a refill.