From Quora: Answer to "Does the ACT or SAT penalize you additional points for getting an answer wrong? Is there a benefit for guessing on questions you don't know on either test?"

https://www.quora.com/Does-the-ACT-or-SAT-penalize-you-additional-points-for-getting-an-answer-wrong-Is-there-a-benefit-for-guessing-on-questions-you-dont-know-on-either-test/answer/John-Linneball

No. Neither one has a “guessing penalty.” The SAT used to, but doesn’t now. So guessing at questions that you don’t know or don’t have time to solve gives you a 1 in 4 chance of getting the right answer just by chance.

NOTE: The SAT subject tests (not the regular SAT) STILL DO have a guessing penalty, where you lose 1/4 of a point for every wrong answer - i.e., not only do you not get the point for that question, but you lose 1/4 of a point you already earned. So DO NOT guess on the SAT subject tests (e.g., Spanish, physics) unless you can eliminate one answer as obviously wrong. Why? Because if you guessed the whole test at random, you’d lose 1/4 of a point 4 times, then get one point the 5th time, which would add up to a net gain of zero. If you can eliminate one answer as wrong, then you’d lose 3/4 of a point (3 * 1/4) for every one you guessed correctly, and end up 1/4 of a point ahead. Hope this helps.