Once your campaign is configured to accept recurring donations, the campaign's donation page will display a checkbox prompting the donor to "Charge me this amount monthly". When selected, the amount-box and total (near the donate button) change to reflect that it is a monthly gift.
Recurring Upgrade Notice
Administrators can add a recurring upgrade notice to their donation page. This notice prompts donors to convert one-time donations into recurring gifts during the donation process. How it works: while the donor is on the donation form, the system detects if they have chosen a one-time gift, and if so displays a fixed notification at the top of the page prompting the donor to convert their donation to a recurring gift of a specified amount relative to the one-time donation amount they entered. This relative amount is managed by the administrator, so it can be the same as the amount they entered, or a percentage, like 25%, of the amount they entered. For example, if the amount entered is "25" (25%) and the donor enters a one-time donation of $50, they will be prompted to convert their donation into a recurring gift of $12.50 (25% of $50).
The recurring upgrade notice, as well as the recurring upgrade amount, can be enabled and set under Forms > Donation Settings > Recurring Donations in the Admin.
Administrators can deploy an A/B test by setting multiple relative amounts to be served to different sets of users. The test results are captured and sent to Google Analytics where they can be analyzed. To deploy an A/B test, enter a comma delimited list of number of users followed by the desired percent for that user set. For example, for the value "50 25, 25 15, 25 10", 50% of users will be prompted to convert their donation to a recurring gift of 25% of their entered donation amount; 25% of users, 15% of the amount entered; and another 25% of users, 10% of the amount entered.