Usually when this happens, the benefit amount is showing a partial year because of the birth date of the individual. It is not a calculation issue. This happens a lot. To test it, look to see what the month of their birthday is and multiply the benefit by how many more months are left after the month of birth.

*Note, benefits start paying out 1 month after the month of birth stated.

*Note, if benefits are starting on 62nd birthday, payout starts 2 months after stated month of  birth

*Note, December birthdays will pay out the next year