What is a widow's full retirement age for survivor benefits? It is not the one you read.

How to read the survivor table in two steps

This page is not legal, tax, medical or financial advice. It sets out the rule so you know what to ask.

The table above has two ages for one woman. The first is your full retirement age for your own benefit. The second is your full retirement age as a widow. For many birth years, they are not the same.

Step one: find your birth year in the left column. Step two: read across to the last column. That is the age at which a survivor benefit can reach its top level.

The rule comes from a footnote. On its normal retirement age page, Social Security says widows whose benefit is based on reaching 60 should add 2 years to the year of birth shown in the table. In plain words, the survivor table runs two years behind.

So a widow born in 1960 has two ages in the same year. Her own is 67. Her survivor age is 66 and 8 months.

Two birthdays that move you to another row

If you were born on January 1, Social Security treats you as born the year before. You read the row above yours. That is not rounding. It changes the age.

There is a second rule for any birthday on the first of a month. Social Security figures your age as if your birthday fell in the month before.

If either one is you, ask Social Security to confirm your date in writing. Do not work it out from a table alone, including this one.

What the percent climbs toward

A widow can start survivor benefits at 60. At 60, the payment starts at 71.5 percent of his benefit. Social Security's survivor amount page gives a few points along the way: over 75 percent at 61, over 80 percent at 63, and over 90 percent at 65.

Waiting until your survivor full retirement age can take you up to 100 percent. That top level assumes something, though. It assumes he did not claim his own benefit early.

If he did, a cap can apply, and waiting past it gains nothing. That rule has its own page: why a widow's benefit stops growing.

Social Security used to post a month-by-month chart. It no longer does. If you need the exact figure for one month, that number has to come from them.

How the cut is spread across the months

Social Security's survivors early chart says a survivor benefit that starts at 60 is always cut by 28.5 percent. That is the 71.5 percent above. The cut shrinks a little for each month you wait, until it is gone at your survivor full retirement age.

So the later your survivor age, the more months the cut is spread over, and the smaller each month's step. Here is the sum, 28.5 percent divided by the months from 60 to your survivor age.

Use it to see the shape, not to plan a date. Your own number, in dollars, comes from Social Security.

The age on the letter in the kitchen drawer

You have read the normal table. Maybe a friend showed it to you, or you found it yourself after the funeral. You were born in 1960, so the row says 67. You do the math and plan to wait.

Nobody told you the table has a second version. It sits in a footnote on an actuary's page. Nobody would think to look there.

Eight months is not small. It is eight months of a benefit at its full level, or eight months of waiting for a level you had already reached.

So write two ages on the same page. Your own, and your survivor age. Then take both to Social Security and ask them to confirm each one against your own record.

Where Nancy Whitaker's book goes from here

This is the problem The Year You Retire was written for. A widow can have a claim on more than one record, and each one has its own rules.

Her Own Record, and the Other Ones has the survivor table shift, the 71.5 percent floor, the nine-month marriage rule and the remarriage rule. Remarrying at or after 60 does not cost you the survivor benefit. It also has the switching rule that is still open to widows, which lets you take one benefit now and move to another record later.

The Age Ladder has the normal table, the January 1 rule and the rule that a husband's delay credits carry into his widow's benefit.

Your First Year Pages gives you a page for the records you might claim on, with a line for the date of death and whether he claimed early.

The best part, we think, is how plain the book is about what it could not confirm. Where Social Security does not state a rule, the book says so and tells you what to ask.