Some creators have opted into charging their patrons as soon as they join (sometimes referred to as "charging up front.")
Since you are charged when you join a creator's Patreon community, you will have access to patron-only content right away and creators can start sending you any rewards that you might have earned. That said, creators may still maintain a monthly reward system, so make sure to double check with them if you're looking for a specific reward.
After your initial immediate charge, all following charges will take place on the 1st of each month. If you become a patron to a creator towards the end of the month, this might come across as a double charge; but the initial charge acts as payment for the month in which you became a patron and the next payment is for the month following.
If you increase your pledge amount for a creator who is charging up front, you are charged the difference between your previous charge and your new pledge amount.
Example: You had a pledge of $10 and you were charged $10 for that pledge. Then you increased your pledge to $15. You are charged $5. You increased your pledge to $16. You are charged $1.
If you decrease your pledge amount to a creator who is charging up front, you are not charged right away when you lower your pledge amount. The new pledge amount will be reflected when your pledge renews at the beginning of the next month.
Example: You had a pledge of $10 and you were charged $10 for that pledge. Then you decreased your pledge to $8. You are not charged anything when you made this change. The next time your pledge renews (at the beginning of next month) you are charged $8.
Note: a hold is placed on all pledges of $100 or greater, which will last for 72 hours. For more details, you can look here.
Are you a creator? Learn more about charging your patrons up front here.