Dey — month 10 of the Persian year

The month at a glance

Month number

10

In Iranian usage

Dey

In Afghan usage

Jadi, or borj 10

Length

30 days

Gregorian window

December 21 to January 21

This month shares its Afghan name with a zodiac sign. What the tradition carries for the sign is on the sign's own page; this page is about the month.

Read about Capricorn, the sign

Dey and Jadi: two naming systems, one month

Month 10 of the Solar Hijri calendar is called Dey in Iranian usage and Jadi in Afghan usage. Both names belong to the same calendar and cover the same days. Neither is the real name and neither is a variant of the other; they are two naming systems for one month.

In Afghan usage the month names are the traditional borj names, which are also the names of the zodiac signs. Alongside the name, a month is commonly referred to by its number. Borj 10 means the tenth month of the year, and the tenth month is Jadi — the same span of days that an Iranian calendar prints as Dey. A reader who asked which month borj 10 is has asked about this month.

Only the names differ. The month boundaries, the month lengths and the leap rule are identical in both systems, so a date written one way becomes the other by changing the name alone.

Where the month sits in the year

Dey, or Jadi, is the tenth month of the Solar Hijri year and the first month of winter. It follows Azar, called Qaws in Afghan usage, and is followed by Bahman, called Dalw.

It runs 30 days, every year. Its length never changes, because the day that a leap year adds falls at the very end of the year, in Esfand — Hut in Afghan usage — and not here. The Persian year opens with its longer months and closes with its shorter ones, and Dey sits in that second stretch, in the coldest part of the year.

Why its Gregorian dates shift

The Solar Hijri year does not begin on a fixed Gregorian day. It begins at the vernal equinox, an astronomical moment that arrives at a slightly different time each year, while the Gregorian calendar absorbs its own leftover fraction of a year with a leap day. The two systems slide against each other by a matter of hours and then settle back.

The month lengths are set by the calendar's own rule, but the start of the year is determined by the equinox. So the Gregorian date on which Dey begins is determined rather than chosen, and it moves — within a narrow window. Across the documented range, the 101 consecutive Persian years from 1329 to 1429, which for this month fall in the Gregorian years 1950 to 2051, the month has begun on 21 to 23 December and ended on 19 to 21 January.

That is why a calendar printed with a single fixed Gregorian range for this month is right in most years and wrong in the rest.

When Dey began

The month lengths are set by the calendar's own rule, but the year starts at the spring equinox — so the Gregorian day this month begins on is not the same every year.

Across the 101 years below, Dey began on 3 different Gregorian dates. A calendar printed with one fixed range is right for most of them and wrong for the rest.

From 1950-12-22 to 2051-01-20.

1. December 21

   20 yearsEnded January 19.

   1996, 2000, 2004, 2008, 2012, 2016, 2020, 2024, 2028, 2029, 2032, 2033, 2036, 2037, 2040, 2041, 2044, 2045, 2048, 2049

2. December 22

   78 yearsEnded January 20.

   1950, 1952, 1953, 1954, 1956, 1957, 1958, 1960, 1961, 1962, 1963, 1964, 1965, 1966, 1967, 1968, 1969, 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1997, 1998, 1999, 2001, 2002, 2003, 2005, 2006, 2007, 2009, 2010, 2011, 2013, 2014, 2015, 2017, 2018, 2019, 2021, 2022, 2023, 2025, 2026, 2027, 2030, 2031, 2034, 2035, 2038, 2039, 2042, 2043, 2046, 2047, 2050

3. December 23

   3 yearsEnded January 21.

   1951, 1955, 1959

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