Genealogy: 1940 U.S. Census birth year reference chart

Birth Year Reference ChartBy Barry J. Ewell
As you track your ancestor through the U.S. Federal Population Censuses, you can use age to help you

  • Identify individual members of the family
  • Provide clues to confirm I have the right person/family unit as you search each census
  • Provide clues as to relationship in the family
  • Provide clues if I have the right female when surnames change through marriage
  • Provide clues when people use nicknames and other name variations from one census to the next

I have prepared a birth year reference chart for each census to help you identify an estimated birth year for each ancestor.  This article will focus on the 1940 U.S. Federal Population Census.

Learn more about information about age found in the census:

1940 U.S. Census birth year reference chart
In Column 11 of the 1940 US Population Census, learn the age of each member of the household.  The following chart will provide the approximate corresponding birth year for the age provided.

Age calculated as of April 1, 1940.

AgeBirth YearAgeBirth YearAgeBirth Year
Mar 0/121940281912671873
Feb 1/121940291911681872
Jan 2/121940301910691871
Dec 3/121940311909701870
Nov 4/121940321908711869
Oct 5/121939331907721868
Sep 6/121939341906731867
Aug 7/121939351905741866
Jul 8/121939361904751865
Jun 9/121939371903761864
May 10/121939381902771863
Apr 11/121939391901781862

Census taker instructions for age on 1940 Census
The following are the exact instructions given to census taker (Enumerator):

458. Column 11. Age at Last Birthday.-Enter the age of the person at his last birthday before 12:01 a.m., April 1, 1940. Thus, a person whose 18th birthday occurred on April 8, 1940, should be reported as 17 years of age because that was his age on his last birthday before April 1, 1940. For persons 1 year old and over, this question calls for the age in completed years at last birthday.

459. Ages of Infants.-The entry in col. 11 for children less than a year old should indicate age in completed months, expressed as twelfths of a year. Ask the following question in each household: “Are there any children in this household who were born on or after April 1, 1939?” For each child born after April 1, 1939, ascertain the actual birth date and determine the proper entry for col. 11 by referring to the table showing ages by birth dates at the foot of the schedule. Thus the age of a child born on May 2, 1939, should be entered as 10/12. Note that a child born after 12:01 a.m., April 1, 1940, is not to be enumerated.

460. Infant Card.-You must fill out an Infant Card (Form P-4), in addition to the line of entries on the Population schedules, for each child born during the 4 months from 12:01 a.m. December 1, 1939, to 12:01 a.m., April 1, 1940. That is, fill out an Infant Card for each child for whom the entry in col. 11 is 0/12, 1/12, 2/12, or 3/12.

461. Note that questions 1 to 10 on this form are to be filled out at the time the enumerator is obtaining information for the Population schedule. The answers to questions 11 to 23 may be copied from the Population schedule at the end of each day of canvassing. The numbers in parentheses at the end of questions 11 to 23 refer to the column numbers on the Population schedule from which the information is to be transcribed.

462. If the infant’s father is not a member of the household in which the infant resides, enter “Not a member of household” in answer to question 14 and leave questions 15 to 19 blank. If the mother is not a member of the household, enter “Not a member of household” in answer to question 20 and leave questions 21, 22, and 23 blank.

463. The completed Infant Cards must be turned in with your portfolio to your Supervisor upon the completion of the enumeration of your district.

464. Ages in Round Numbers.-The age of the person will sometimes be reported in a round number, like 30 or 45, or “about 50” when that is not the exact age. If an age ending in “0” or “5” is reported, you should inquire whether that is really the exact age. If, however, the exact age is not know, enter the approximate age, rather than “Unknown.”