Social Security's Primary Insurance Amount: What Is It?

Do you know how much you're going to get in Social Security? Probably not. According to a recent survey by Nationwide, 63% of would-be retirees confess they don't know how Social Security works, and even more scary, the average worker estimates they'll bring in $1,628 per month in benefits, which is 30% more than current retirees say they collect.

Overestimating your benefit can throw your retirement savings strategy out of whack. To keep that from happening, it can help to understand Social Security's complex calculation and more specifically, how Social Security determines your primary insurance amount, or the amount of money you can draw from Social Security at your full retirement age.

Let's clear up the confusion

Social Security is designed to replace 40% of workers pre-retirement income in retirement. However, the way that Social Security is calculated means that the amount you actually receive in retirement may be much higher or lower than that percentage.

A question mark rests on $100 bills spread out on a table.
A question mark rests on $100 bills spread out on a table.

IMAGE SOURCE: GETTY IMAGES.

A pay-as-you-go program, Social Security payments are financed by payroll taxes on current workers, but not all of a worker's income is subject to these taxes. In 2018, payroll taxes only apply on income up to $128,400. Because there's a cap on taxes, there's also a cap on the amount you can receive in benefits.

The amount of money you make every year that's subject to taxes is important, because Social Security ultimately determines how much you'll receive in benefits based on the average inflation-adjusted income you earned during your 35-highest earning years of work.

Specifically, Social Security begins its calculation by coming up with your average indexed monthly earnings (AIME).

To determine your AIME, your historical annual earnings are adjusted for inflation using Social Security's average wage index (AWI), an index that tracks national changes in wages with a two-year lag. Specifically, your historical income will be indexed based on the AWI reading for the year two years prior to the age you turn 62 -- the earliest age at which you can claim Social Security.

For instance, the historical earnings for a person turning age 62 in 2018 are indexed based on the 2016 AWI figure of $48,642.15. To adjust their historical income, Social Security divides $48,642.15 by the AWI for each year of earnings to get an indexing factor for each year. Once that's done, it multiplies each year of the person's earnings by the factor for that year to get an inflation-adjusted earnings amount. Then, it sorts out and sums up the highest 35 years of income and divides that number by 420, or the number of months in 35 years, to come up with your AIME.