[webstartupper]

One way to decide on the free trial duration is by asking yourself - what is the shortest amount of time that my typical customer will find the "aha" moment using my software. This could be as little as one day and as much as 90/120 days depending on what the software does.

One benefit of a shorter trial is that it lets you iterate fast - if your trial period is just 7 days, you could make a change and see its result in 7 days.