It doesn't throw things off for future payments — it just makes it so that on short months the payment is taken slightly earlier/later. This is presumably not a

It doesn't throw things off for future payments — it just makes it so that on short months the payment is taken slightly earlier/later. This is presumably not a core part of your business, and you're spending a lot of time thinking about it. I would google to see how others have handled this problem and just do what they do. Otherwise you are spending too much time reinventing the wheel for a presumably-ancillary part of your business. If someone subscribes during a short month, they are always billed on that day of the month. If someone subscribes during a month with more than 28 days, they are always billed on that day of the month during months with sufficient days. During months without sufficient days, they are billed on the first of the following month. When that happens, they will be billed twice during the long month and zero times during the preceding short month. No one should mind this. Option 1 will seem identical to most users, but some may notice. Why not give them 31 days though? That way no one can complain.