In the US, you can refer to the FTC guide on pre-sales warranties for insight. Clearly spelling out what defines the start of service is key.
Example: with a 30 day satisfaction guarantee - is start of service defined as:
Of course, a published warranty section reviewed by a competent lawyer is helpful in addressing these scenarios.
There are 3 different things here:
So, every company has a different official policy, the customer has options to get money back even not under the company's policy and many companies don't really operate according to their official policy.
My suggestion is, if you are running a software (or other digital product) company, is to always offer a 30 day (or more) guarantee and to be very specific about it's conditions in your terms of use - then, when someone asks for a refund just give it to them even if they aren't entitled to it according to your conditions.
In the US, Federal Law allows the consumer 60 days from the date of their billing statement date to contest the charges. When you bill them is not relevant, except in extending the time.
So if the customer starts their subscription on the 1st, and you bill on that date (which means that the charge clears on the 2nd), and the credit card company issues their statement to the customer on the first- your charge won't show up until the next billing cycle, 30 days later. And the customer has 60 days after that to contest the charge.
So, in practice, the consumer can have from 60 - 90 days to issue a chargeback on your service (unless the card was present at the time of transaction).
In three separate companies now, I have offered 30 and 60 day money back guarantees and I can't remember a single request for a refund. I am sure there was at least one, but the point is: they're rare.
If you have a legit product and offer a money back guarantee, my experience tells me the request for refund might be an edge case and the rule for business is -- don't optimize the edge cases. Be generous with your refund and be liberal on your interpretation. If somebody asks for a refund on day 45, refund the whole thing -- all 45 days. On day 90, offer to refund their last 30 days. Etc.