I tried to post before on this thread but alas......
You can now earn up to 100% towards retirement, a former squadron skipper of mine who did 11 years as a CWO in the Army and my former boss who just retired as a USMC Colonel after 40 years are both earning over 75% of their pay. They way they were both able to do it is that they had prior service, the Marine was enlisted and CWO before becoming a regular officer and went to 40 and is now earning 100% retirement, he mentioned that they had changed the law in 2006. If someone has prior service and they make O-6 it would be pretty easy for them to go over 30 and earn the extra retirement, I believe HYT for an O-6 being 30 years of
commissioned service. Apparently you can earn more than 100% but the only people I believe who are going to be able to do that are 3 and 4 star GO/FOs since they are appointed, I don't think MCPON and his service equivalents can exceed 40. I think everyone else has to retire when they hit 40, even if they have not hit HYT yet.
I cannot find the law but
here is a link that mentions the 100% and beyond.