Understanding the Social Security Benefit Calculation

Most benefits provided by social security are determined in relation to your primary insurance amount.

The retirement benefit you’ll receive if you retire at yourfull retirement age is called your primary insurance amount(or PIA). Most of your other benefits (and benefits your family members receive based on your earnings) are determined relative to your PIA. For example, if you take early retirement, your benefit will be a reduced percentage of your PIA.

The calculation of PIA is somewhat complicated, and few people will want to actually calculate their own number. Yet it’s useful to have a general idea how your PIA is generated. This article provides an outline of the calculation. A later article explains how an additional year of earnings will affect your benefit.

In a nutshell: The calculation looks at your entire earnings history with inflation adjustments, chooses the 35 best years and finds your average indexed monthly earnings for those years. Then it applies a formula that typically comes to somewhere between 25% and 45% of this inflation-adjusted average.

Step 1: Taxed Social Security Earnings

The first step is to find your taxed social security earnings for every year in your work history, beginning with the year after the year you turn 21. You should receive a statement with these amounts each year beginning at age 25. Note that the calculation only includes earnings that were subject to social security tax. For example, if you earn $100,000 in 2005, your taxed social security earnings for that year will be $90,000, because that is the maximum amount on which you have to pay social security tax for that year.

As always in the social security system, earnings are wages and net earnings from self-employment. Other types of income, such as investment income, are not included.

Step 2: Inflation Adjustment

Next, increase the earnings for earlier years to reflect inflation. For example, $10,000 you earned in 1977 would be equivalent to $34,000 earned in 2002. Each year has its own inflation adjustment: you would get a bigger adjustment for wages earned in 1976 and a smaller inflation adjustment for wages earned in 1978. As a result, this part of the calculation requires a table of inflation adjustments — and the table itself changes each year.

The indexing year is normally the year you turn 60, even if you start receiving benefits at age 65 or later. If you die or become disabled before age 62, the indexing year will be two years before the year of your death or disability.

Step 3: Select the 35 Highest Years

Next, select the 35 highest years based on the inflation-adjusted amounts. If you earned $10,000 in 1977 and $30,000 in 2002, your earnings for 1977 would rank higher because they are equivalent to $34,000 in 2002 earnings. If you don’t have 35 years with earnings, the calculation will include some years at zero earnings.

Step 4: Find the Monthly Average

Next, add up all the inflation-adjusted amounts for the 35 years that were selected and divide by 420 (the number of months in 35 years). In the world of social security, this is known as your average indexed monthly earnings (AIME).

The calculation uses a smaller number of years for someone who dies or becomes disabled before age 62.

Step 5: Apply the Benefit Formula

A three-tiered benefit formula determines a monthly benefit based on your AIME. It is designed to replace a higher percentage of earnings for people at lower levels. At higher levels of earnings the formula provides higher benefits, but the percentage of the benefit relative to AIME declines.

The earnings levels where percentages change are called bend points because a graph of the benefits would have a bend in the line at those points.

The formula provides 90% of AIME up to the first bend point, 32% from there up to the second bend point, and 15% above the second bend point. Bend points are adjusted each year for inflation. For workers retiring in 2005, the bend points are $627 and $3,779. Note that these are applied to your monthly earnings, so they correspond to annual income 12 times that amount ($7,524 for the first bend point and $45,348 for the second bend point).

Example 1: Your AIME is $2,844. If you retire in 2005 your PIA would be  .9(627) + .32(2,844 – 627) = $1,273.74 (before rounding). This is the monthly retirement benefit you receive if you retire at full retirement age.

Example 2: Your AIME is $3,985. If you retire in 2005 your PIA would be .9(627) + .32(3,779 – 627) + .15(3,985 – 3,779) = $1,603.84 (before rounding).

The practical impact of this formula is that a worker with lower wages might expect to receive a social security benefit that replaces about 45% of those wages on an inflation-adjusted basis, assuming the worker retires at full retirement age. A worker with much higher earnings will receive a larger social security benefit, but it may replace only about 25% of covered wages.

Earnings that are above the social security wage base ($90,000 for 2005) don’t count in the formula. If your earnings are significantly above that level, your social security benefit will replace a much smaller percentage of your wages.


The discussion here deals with the main rules for calculating your primary insurance amount. It omits special rules that can apply in various circumstances, such as a reduction in benefits that can apply when you earn a retirement benefit while performing work that isn’t covered by social security. Bear in mind also that your actual benefit isn’t the same as your PIA if you retire before (or after) you reach full retirement age, as explained here.

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