Likely, liable, apt, prone and calculated are all used as words denoting probability. They have their different nuances, which should be respected by those who care about treating words in a discriminating way.
Apt and prone imply that the probability arises from the disposition of the subject, and usually connote faults or weaknesses. "He is apt to take offence" "She is prone to tears." Liable also suggests that the subject is likely to suffer from something prejudicial. "It is liable to break when you put a strain on it." "He is liable to have a fit if you excite him." Likely is colourless. Unlike the others, it contains no suggestion of habit but may refer to a single event. Nor does it imply that the probability arises from the subject's disposition; the probability may be in the nature of things. "Today is likely to be fine." "He is likely to make a success in the job." The suggestion in calculated is of judgment in the light of full knowledge; in the words not calculated judgment is passed on an unsuccessful design. "He took elaborate precautions, but they were not of a kind calculated to be successful."