(via The Wall Street Journal's Jim Blankenship: http://blogs.wsj.com/experts/2015/01/23/how-people-misread-their-social-security-benefit-statements/)
"For many, Social Security benefits will play a significant role in the retirement income scheme. The problem is that the Social Security system is hard to understand–it’s difficult to know for sure what benefits you’ll have coming to you. The Social Security Administration provides a statement of your benefits to help with the planning process. The problem is that there are assumptions made for the statement’s estimates, and these assumptions result in misunderstanding the statement’s intent. The numbers on my statement are the benefits I’ll receive. The problem is that SSA doesn’t know when you’re planning to retire, or rather when you’ll stop working, so they must make an assumption with the benefit numbers that they provide on your statement. The assumption is that you will continue working and earning the same amount as the most recent year reported, from now until the age listed on the statement. Of course, that’s rarely the case.
If you’re under age 62 your Social Security statement will list an amount for your age 62, your full retirement age (ranging between age 66 and age 67), and age 70. If you leave full-time work and don’t earn the same as you earned in the most recent report, your earnings history will be different from what was assumed. If your earlier earnings history had lower amounts in it (or perhaps some zero years), there could be a difference between what your statement said and what you actually receive in benefits.
SSA has tools available on their website (www.SocialSecurity.gov) to help you estimate your benefit using more realistic future anticipated earnings. There are commercial packages available to assist with this as well. Using such a calculator won’t be flawless, but it can help you to more accurately estimate your future benefits.
The numbers on my statement are the ONLY benefits I’ll receive. As mentioned above, your SSA statement projects your own benefit estimates at age 62, full retirement age, and at age 70. What is not included are any additional benefits that you might be eligible to receive. This is especially true if you are married or were previously married and are now divorced or widowed.
If you are married you’re likely eligible for a Spousal Benefit based on your spouse’s Social Security record. If you were married for at least 10 years and are now divorced, you also may have this benefit available.
In addition, if you are a widow(er) you may have a survivor’s benefit available to you based upon your late spouse’s (or late ex-spouse’s) record."