Scenario: you’re using opensource software and you aren’t donating yet, however you have enough money left over every month to do so. Something(s) is holding you back from donating. Think about what that is and what would have to change for you to change that.
Just a note to add, a yearly donation schedule can also be good, as it can reduce payment transfer fees. But on the flip side, if a donatoe wants to stop donating, it’s easier for a yearly payment to fly under the radar.
I think the best option is to offer both yearly and monthly options when possible