Contents   Fixed field   Access points   0xx   1xx   2xx   3xx   4xx   5xx   6xx   7xx   8xx   9xx   Control subfields

045  Time Period of Content (NR)

Input Standards

1st Indicator  Type of time period in subfield ‡b or subfield ‡c
blank character Subfield ‡b or ‡c not present
0 Single date/time
1 Multiple single dates/times
2 Range of dates/times
2nd Indicator  Undefined
blank character Undefined
Subfields (R=Repeatable  NR=Nonrepeatable) Input Standards
‡a Time period code (R) Required if applicable/Required if applicable
‡b Formatted 9999 B.C. through C.E. time period (R) Required if applicable/Required if applicable
‡c Formatted pre-9999 B.C. time period (R) Required if applicable/Required if applicable


A time period code (subfield ‡a) and/or a formatted time period (subfields ‡b and ‡c) associated with the item described in the bibliographic record.

Determine the appropriate values by examining the item. Use the primary source of bibliographic information (e.g., title page), prefatory material, table of contents, and summary statements. In addition, subject headings may indicate chronological coverage. Be as specific as possible.

Do not use for any item for which a chronological approach would not be a logical or common approach to the subject matter. Do not use for the following:

  • Biography, unless a time period is specified on the piece or in a subject heading
  • Collections or anthologies of literature, unless they indicate a clearly delineated time period
  • Comprehensive histories of a subject or a country that cover more than 500 years
  • Dictionaries, encyclopedias, glossaries, catalogs, and gazetteers intended to be nonhistorical in approach
  • Genealogies and family histories
  • Handbooks, manuals, and "how-to" books

Indicate the style period of the composition by coding the decade and/or date of composition in field 045. If you cannot determine the decade or date of composition, use an estimate of the range of years. Estimate the chronological code based on evidence in or on the piece in hand. You may estimate codes from a composer's dates.


If the date is a date of filming, broadcast, or recording, use field 033 (Date/Time and Place of an Event).

1st Indicator

Type of time period in subfield ‡b or subfield ‡c. A value that indicates whether a subfield ‡b or subfield ‡c is present and when subfield ‡b or ‡c is present, the type of time period it contains. The values distinguish among a single date/time, multiple single dates/times, and a range of dates/times.

blank character

Subfield ‡b or ‡c not present. Neither subfield ‡b nor ‡c is present.

651   0 Egypt ‡x Economic conditions ‡y To 332 B.C.
045     a0d6

Single date/time. Subfield ‡b and/or ‡c is present, and it contains a single date/time.

650   0 Lunar petrology.
045 0   ‡c 2500000000

Multiple single dates/times. Multiple ‡b and ‡c subfields are present and each contains a date/time. A range of dates/times is identified by value 2 (Range of dates/times).

045 1   ‡b d1972 ‡b d1975
[1972 and 1975]

Range of dates/times. Two ‡b and ‡c subfields are present and contain a range of dates/times. Multiple single dates and/or times are identified by value 1.

650   0 Shenandoah Valley Campaign, 1864 (May-August)
045 2   ‡b d186405 ‡b d186408
650   0 Aurignacian culture.
045 2   ‡c 25000 ‡c 15000

2nd Indicator

Undefined. The 2nd indicator position is undefined and contains a blank ( blank character ).

blank character



‡a Time period code

The four-character time period code. The first two characters represent the earliest period covered. The last two represent the latest period covered. If a single two-character code encompasses the entire period, enter the code twice. Use the following guidelines with the table below:

  • B.C. (Before Common Era) dates. Use a lowercase alphabetic character to represent the millennium and a digit to represent the century. If the century is not known, enter a hyphen instead of a digit.
    650   0 Bronze age.
    045     a-c-
    [3000–100 B.C.]
    651   0 Egypt ‡x History ‡y Eighteenth dynasty, ca. 1570-1320 B.C.
    045     c4c6
    651   0 Rome ‡x History ‡y Republic, 265-30 B.C.
    045     d7d9
    [3000–1000 B.C.]
  • C.E. (Common Era) dates. Use a lowercase alphabetic character to represent the century and a digit to represent the decade. If the decade is not known, enter a hyphen instead of a digit. If more than one time period code applies, enter each in a separate subfield ‡a.
    650   0 Bhopal Union Carbide Plant Disaster, Bhopal, India, 1984.
    045     x8x8
    650   0 Catalan literature, ‡y 16th-18th centuries.
    045     t-v-
    650   0 Civilization, Modern ‡y 20th century.
    045     x-x-
    650   0 Twenty-first century ‡x Forecasts.
    045     y-y-
    651   0 Great Britain ‡x History ‡y Medieval period, 1066-1485.
    045     o6s8
    651   0 Greece ‡x History ‡y 146 B.C.-323 A.D.
    045     d8h2
Time period code table
B.C. table   C.E. table
Time period Code   Time period Code
before 2999 a0   1–99 e
2999–2900 b0   100–199 f
2899–2800 b1   200–299 g
2799–2700 b2   300–399 h
2699–2600 b3   400–499 i
2599–2500 b4   500–599 j
2499–2400 b5   600–699 k
2399–2300 b6   700–799 l
2299–2200 b7   800–899 m
2199–2100 b8   900–999 n
2099–2000 b9   1000–1099 o
1999–1900 c0   1100–1199 p
1899–1800 c1   1200–1299 q
1799–1700 c2   1300–1399 r
1699–1600 c3   1400–1499 s
1599–1500 c4   1500–1599 t
1499–1400 c5   1600–1699 u
1399–1300 c6   1700–1799 v
1299–1200 c7   1800–1899 w
1199–1100 c8   1900–1999 x
1099–1000 c9   2000–2099 y
999–900 d0   (Add 0, 1, 2 ... 9 for the decade)
899–800 d1      
799–700 d2      
699–600 d3      
599–500 d4      
499–400 d5      
399–300 d6      
299–200 d7      
199–100 d8      
99–1 d9      

Period covered Time period code
423 B.C.–390 B.C. d5d6
to 300 B.C. a0d6
42 B.C.–A.D. 37 d9e3
1066–1328 o6r2
12–14th centuries p-r-
1740–1840 v4w4
1828–1859 w2w5
20th century x-x-
Compare 1st century A.D. and 20th century e-e- ‡a x-x-
Collected scores of George Gershwin's musical comedies x2x3
‡b Formatted 9999 B.C. through C.E. time period

A specific time period formatted as yyyymmddhh preceded by code c for B.C. or code d for C.E. The era and year are required. The month, day, and hour (based on the 24-hour clock) are optional.

Enter only known elements with a five-character minimum. Use subfield ‡a if you cannot determine the first five characters.

Enter each 9999 B.C. through C.E. time period associated with the heading in a separate subfield ‡b.

651   0 China ‡x History ‡y 221 B.C.-960 A.D.
045 2   d7n6 ‡b c0221 ‡b d0960
651   0 France ‡x History ‡y Revolution, 1791-1797.
045 2   ‡b d1791 ‡b d1797
651   0 Japan ‡x History ‡y February Incident, 1936 (February 26)
045 0   ‡b d19360226
‡c Formatted pre-9999 B.C. time period

A formatted time period consisting of as many numeric characters as are needed to represent the number of years B.C. Enter each pre-9999 B.C. time period associated with the heading in a separate subfield.

650   0 Geology, Stratigraphic ‡y Mesozoic.
045 2   ‡c 225000000 ‡c 70000000

This page last revised: September 2, 2015