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

045  Time Period of Content (NR)

Record Type


Input Standards

1st Indicator  Type of time period in subfield ǂb or subfield ǂc
blank character Subfield ǂb or ǂc 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
ǂa Time period code (R) Required if applicable/Required if applicable
ǂb Formatted 9999 B.C. through C.E. time period (R) Required if applicable/Required if applicable
ǂc Formatted pre-9999 B.C. time period (R) Required if applicable/Required if applicable
ǂ6 Linkage (NR) System supplied/System supplied
ǂ8 Field link and sequence number (R) Optional/Optional


A time period code (subfield ǂa) and/or a formatted time period (subfields ǂb and ǂc) 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 ǂb or subfield ǂc. A value that indicates whether a subfield ǂb or subfield ǂc is present and when subfield ǂb or ǂc 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 ǂb or ǂc not present. Neither subfield ǂb nor ǂc is present.

045     a0d6
651   0 Egypt ǂx Economic conditions ǂy To 332 B.C.

Single date/time. Subfield ǂb and/or ǂc is present, and it contains a single date/time.

045 0   ǂc 2500000000
650   0 Lunar petrology.

Multiple single dates/times. Multiple ǂb and ǂc 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   ǂb d1972 ǂb d1975
[1972 and 1975]

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

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

2nd Indicator

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

blank character



ǂa 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.
    045     a-c-
    650   0 Bronze age.
    [3000–100 B.C.]
    045     c4c6
    651   0 Egypt ǂx History ǂy Eighteenth dynasty, ca. 1570-1320 B.C.
    045     d7d9
    651   0 Rome ǂx History ǂy Republic, 265-30 B.C.
    [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 ǂa.
    045     x8x8
    650   0 Bhopal Union Carbide Plant Disaster, Bhopal, India, 1984.
    045     t-v-
    650   0 Catalan literature, ǂy 16th-18th centuries.
    045     x-x-
    650   0 Civilization, Modern ǂy 20th century.
    045     y-y-
    650   0 Twenty-first century ǂx Forecasts.
    045     o6s8
    651   0 Great Britain ǂx History ǂy Medieval period, 1066-1485.
    045     d8h2
    651   0 Greece ǂx History ǂy 146 B.C.-323 A.D.
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- ǂa x-x-
Collected scores of George Gershwin's musical comedies x2x3
ǂb 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 ǂa 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 ǂb.

045 2   d7n6 ǂb c0221 ǂb d0960
651   0 China ǂx History ǂy 221 B.C.-960 A.D.
045 2   ǂb d1791 ǂb d1797
651   0 France ǂx History ǂy Revolution, 1791-1797.
045 0   ǂb d19360226
651   0 Japan ǂx History ǂy February Incident, 1936 (February 26)
ǂc 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.

045 2   ǂc 225000000 ǂc 70000000
650   0 Geology, Stratigraphic ǂy Mesozoic.
ǂ6 Linkage

Data that link fields when non-Latin script is entered. This subfield is system supplied and does not appear in OCLC online displays. Do not add subfield ǂ6. For more information about subfield ǂ6, see Control Subfields.

ǂ8 Field link and sequence number

For information about subfield ǂ8, see Control Subfields.


Field 045 is not indexed.

This page last revised: October 13, 2017