Letter Percent (until August 2010)[2] Percent (since September 2010)[3] 4+ 90%–100% 95%–100 4 85%–89% 87%–94% 4- 80%–84% 80%–86% 3+ 77%–79% 3 73%–76% 3- 70%–72% 2+ 67%–69% 2 63%–66% 2- 60%–62% 1+ 57%–59% 1 53%–56% 1- 50%–52% R 0%–49%