How can I set up a recurring monthly donation?

Is it possible to set up Jotform to accept recurring monthly donations? 

Yes that's possible and your setup would highly depend on how much the donations will be (or if it's something that is upon your user's discretion).

1. If it's a fixed donation, say $10 per month, then just setup your Paypal Payment Field to SELL SUBSCRIPTIONS. Yes, you're aiming for DONATIONS but if you need recurring payments, you'd need to use SUBSCRIPTIONS.

2. And if you need something that will allow your users to key in their preferred donation amount, just enable the VARIABLE PRICE option when adding your SUBSCRIPTION.

Here's an example form https://form.jotform.com/71015271238953 showing both of them (fixed and variable recurring donation).

Related guides:

How-to-Setup-a-Recurring-Payment-Option

How-to-Have-a-Recurring-Custom-Donation-Payment-Form