I was born 3/30/49. I decided to wait until age 70 (3/30/2019) to collect SS benefits. ssa.gov says my benefit at 70 will be $3423. I'm assuming that with the 2.8% increase, it will be $3518, which should show up on the ssa site on 12/1/18.
After a ton of reading, I'm still confused about when to actually apply in order to ensure I get the maximum benefit. My current understanding is that I should apply 3 months before I want to start collecting, so I should apply to 12/30/2018, right? I also read that my first month of actual eligibility will be 4/2019 and that that payment will be made on the fourth Wednesday of 5/2019, since SS pays in arrears.
Do I have all this right? And how to I ensure on my application that I want to start collecting as of my 70th birthday, and not before?
No. If you turn age 70 on March 30 2019, Social Security would pay you your full age 70 rate if you claim your retirement benefits starting with March 2019. That would be the payment that Social Security normally makes on the 4th Wednesday of April 2019 in your case, since you were born after the 20th of the month (https://www.ssa.gov/pubs/EN-05-10031-2019.pdf). You could choose not to claim your benefits until April 2019, but your benefit rate would be no higher if you do so. So, you would simply be passing up a full monthly benefit payment for no net gain.
The exact date that you file your application isn't important. You're allowed to file an application as early as 4 months prior to the month that you want to start your benefits, so an application for benefits starting effective March 2019 could be filed as early as November 1 2018. You shouldn't need to do anything special to assure getting your full age 70 rate, other than specifying March 2019 in your case as your month of election to start your benefits.