<p>The base cost of the subject test registration is $20 and you are charged $9 for each test. If you decide to add a test, you pay $9.00 more. However, you don’t have to pay at the time; you can pay later and they’ll hold your scores until you scrape together the cash.</p>
<p>The only surprise that you might come up against is if you take a language test; they can charge you $20 for those; since they require special equipment, it’s unlikely that you’ll have the opportunity to switch to it if you didn’t sign up for it in the first place since they might need a tape recorder, headphones, etc.</p>
<p>Exactly. The CollegeBoard doesn’t care which or how many tests you sign up, except for language tests that require special equipment. You can pick History and English for the test day, and end up doing Math I, Math II, and Chemistry once you actually get there (that’s just an example), and you will only pay the extra $9.00 for the third subject test (Whatever it is) unless it’s a language that costs $20.00, and you won’t pay that at the testing center but sometime later when you get a bill, so don’t think that you have to carry around spare change with you to the testing center in case you change your mind! </p>
<p>I called CB and they confirmed that you don’t have to pay any late fees to add an additional test and the fee for the additional test is the regular additional test fee ($9 for many tests). You just tell them on the AM of the test. All this assumes that you have registered for at least one test already</p>