This can be configured within the donation level settings in the donation form.
  1. Select Fundraising > Donation Management
  2. Select All Donation Forms
  3. Find your donation form and click Edit
  4. Click Next
  5. Click Edit next to the donation level that should be configured with the dynamic ask
  6. Mark the checkbox next to "Calculate a dynamic donation ask amount using the formula specified"
  7. Look under "For donors who are logged in, start with the value of this field on the constituent's record"
  8. Select Additional Information > desired custom field
    • Note: Only monetary fields will appear in this list
Related topic

How do I add additional fields to the constituent profile?