We rely on the Master Beneficiary File to document a number of facts regarding claiming of Social Security benefits and quality of date of birth data in administrative files. We then assess the impact of changes in retirement incentives that have taken place since 2000 on claiming. We find evidence of non-trivial misreporting or clerical errors in the dates of births that give rise to systematic patterns but nevertheless appear to be fairly random. We also confirm significant tendency to claim in January or on birthdays, but we find that these patterns are still sensitive to incentive effects. Relying on the discontinuity in the Early Entitlement Age that occurs for people born on the second day of any month, we find evidence that people do not have singlepeaked preferences over claiming age: relaxing the early retirement constraint leads to acceleration of retirement by some people for whom the constraint would not be otherwise binding. One possible explanation for this pattern is a preference for retiring at one’s birthday. We take advantage of a change in the full retirement age and find that there remains unusually large (relative to other birthdays) number of people who claim around their 65th birthday, supporting the idea that Medicare eligibility has an impact on claiming retirement benefits. Finally, we confirm that elimination of the earnings test in 2000 for those above full retirement age accelerated retirements and find that it also led to a significant weakening of the January effect in that group, bolstering the idea that the January effect is sensitive to economic incentives.