How to use fill_in with find in Capybara (if possible)

If you have a reference to the element itself you'd use set instead of fill_in:

find(:css, "input[id$='donation_pledge_hundreds']").set("10")

However for your specific example, fill_in should be able to find the element as you know it's ID:

fill_in 'donation_pledge_hundreds', with: "10"

element = find(:css, "input[id$='donation_pledge_hundreds']")   
element.fill_in with: "10"

Instead of a method, you can use brackets to return :name or :id, e.g. element = find(:css, "input[id$='donation_pledge_hundreds']") fill_in element[:name], :with => "10" The same approach can be used with select - select my_type, from: find('select[name$="[type]"]')[:name]