From letter Jan 26, 2018.
"So essentially he will lose out on ~$50 a month from May 2018-Dec. 2018 that he earned by delaying (approx $400), as Social Security does not reimburse that lost money if you file mid-year."
This must be wrong. I thought you would get a lump sum the next time SS does their adjustments

Hi,

What this person stated in their question is essentially accurate. When a person files for Social Security benefits between full retirement age (FRA) and age 70, Social Security credits their delayed retirement credits (DRC) earned on a calendar year basis. For example:

Bob was born in March 1951, so he reached full retirement age (FRA) in March 2017. Bob delays drawing his Social Security retirement benefits until he turns age 67 in March 2018. Although Bob will have earned 12 months of DRCs, Social Security will initially calculate his benefit rate crediting only the 10 months of DRCs that Bob earned from March 2017-December 2017. They will subsequently recalculate Bob's benefit rate to give him credit for the additional 2 months of DRCs (i.e. January-February 2018), but the increase is not effective until Bob's payment for January 2019. Social Security would pay any back pay due retroactive to January 2019, but not for March 2018 through December 2018 because no rate increase would apply for those months.

Best, Jerry