Islamic months in most countries begin with an actual moon sighting, so the observed date can differ by a day or two from Umm al-Qura (Saudi Arabia's official calendar) and more from the tabular calendar.
Hebrew and Islamic days begin at sunset; the date shown is the one that covers daytime on the Gregorian date.
Sunday, 27 September 2026 (Gregorian) is 14 September 2026 in the Julian calendar, 16 Rabi al-Thani 1448 AH (Umm al-Qura), 16 Tishrei 5787 in the Hebrew calendar, 5 Mehr 1405 AP and 5 Ashvin 1948 Saka.
How far the Julian calendar lags the Gregorian (days, on 1 March)
The same day in each calendar (7 rows)
Calendar
Date
Method
Gregorian
27 September 2026
Proleptic Gregorian day count
Julian
14 September 2026
Arithmetic (Richards)
Islamic (Umm al-Qura)
16 Rabi al-Thani 1448 AH
ICU tables, observational basis
Islamic (tabular)
14 Rabi al-Thani 1448 AH
30-year arithmetic cycle, civil epoch
Hebrew
16 Tishrei 5787
ICU, fixed arithmetic calendar
Persian
5 Mehr 1405 AP
ICU
Indian national
5 Ashvin 1948 Saka
ICU, Saka era
How it's calculated S
Julian Day Number
JDN=N(27 September 2026)+2440588=20723+2440588=2461311
JDN counts days from 1 January 4713 BC (Julian); N counts from 1 January 1970.
This gives 14 September 2026 (Julian); in 2026 the Julian calendar runs 13 days behind the Gregorian.
Other calendars
Islamic, Hebrew, Persian and Indian dates come from the ICU calendar engine in your browser (CLDR), read at noon UTC on the Gregorian date.
About the calendar converter
Every conversion passes through the Julian Day Number, the astronomers' running count of days, which is 2,461,056 on 15 January 2026. Julian-calendar dates use E. G. Richards' arithmetic from the Explanatory Supplement to the Astronomical Almanac. Islamic, Hebrew, Persian and Indian national dates come from the ICU calendar library built into your browser, read at noon UTC on the Gregorian date.
People use it for religious dates, for Iranian or Israeli documents, and for historical records written in the Julian calendar. 15 January 2026 is 26 Rajab 1447 AH in the Umm al-Qura calendar, 26 Tevet 5786 in the Hebrew calendar, 25 Dey 1404 in the Persian calendar and 2 January 2026 in the Julian calendar, which runs 13 days behind from March 1900 to March 2100.
Islamic months in most countries start with a moon sighting, so the date observed locally can differ by a day or two from Umm al-Qura. Hebrew and Islamic days begin at sunset; the date shown is the one covering the daytime.
Worked examples
15 January 2026 in every calendar
Starting from
Gregorian date
Gregorian date
2026-01-15
Show first
Islamic (Umm al-Qura)
Converted date
26 Rajab 1447 AH
Julian
2 January 2026
Hebrew
26 Tevet 5786
Persian (Solar Hijri)
25 Dey 1404 AP
Indian national (Saka)
25 Pausha 1947 Saka
Julian Day Number
2461056
Day of the week
Thursday
Checked against: Aladhan API gToH (Umm al-Qura) = 26 Rajab 1447; Hebcal converter = 26 Tevet 5786; Persian from Nowruz 1404 = 21 Mar 2025 with 31/30-day months; Saka from Chaitra 1 = 22 Mar 2025; JDN = Python date.toordinal() + 1721425
Islamic New Year 1447: observational and tabular differ
Starting from
Gregorian date
Gregorian date
2025-06-26
Show first
Islamic (tabular)
Islamic (Umm al-Qura)
1 Muharram 1447 AH
Converted date
29 Dhu al-Hijjah 1446 AH
Checked against: Aladhan API (Umm al-Qura) = 1 Muharram 1447; tabular date from a separate Python implementation of Reingold & Dershowitz's arithmetic Islamic calendar (civil epoch 16 July 622 Julian)
The day after the last Julian day in Rome
Starting from
Julian date
Julian date (YYYY-MM-DD)
1582-10-05
Show first
Gregorian
Converted date
15 October 1582
Julian Day Number
2299161
Day of the week
Friday
Checked against: Inter gravissimas (1582): Julian 4 October was followed by Gregorian 15 October; Python date(1582,10,15).toordinal() + 1721425 = 2299161
Enter the Gregorian date and pick Islamic (Umm al-Qura) under Show first; the tabular Islamic date is shown alongside. A Hijri year has 12 lunar months and 354 or 355 days, so Islamic dates arrive about 11 days earlier each Gregorian year. The Umm al-Qura calendar puts 1 Ramadan 1447 on 18 February 2026 and 1 Muharram 1448, the Islamic New Year, on 16 June 2026.
Why is the Julian calendar 13 days behind the Gregorian?
The Julian calendar adds a leap day every fourth year, including century years such as 1700, 1800 and 1900, which the Gregorian calendar skips. The gap was 10 days at the 1582 reform, 11 from 1700, 12 from 1800 and 13 from 1900, and it becomes 14 in March 2100. Churches that keep the Julian calendar celebrate Christmas on 25 December Julian, which is 7 January Gregorian.
What is the Julian Day Number?
A continuous count of days that starts at 1 January 4713 BC in the Julian calendar, used by astronomers to subtract dates across calendars without month arithmetic. It is not the same thing as a date in the Julian calendar. Noon UTC on 1 January 2000 is Julian Day 2,451,545, and a Gregorian date converts by adding 2,440,588 to its count of days since 1 January 1970.
When do the Hebrew, Persian and Indian national years begin?
The Hebrew year begins on 1 Tishrei, Rosh Hashanah: 5787 began on 12 September 2026, at sunset the evening before. The Persian year begins at Nowruz, which is set by the March equinox; 1405 began on 21 March 2026. The Indian national (Saka) year begins on 1 Chaitra, 22 March in common years and 21 March in leap years; Saka 1948 began on 22 March 2026.
How accurate is the calendar converter?
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 6 worked examples whose answers come from independent sources; for example, “15 January 2026 in every calendar” is checked against Aladhan API gToH (Umm al-Qura) = 26 Rajab 1447; Hebcal converter = 26 Tevet 5786; Persian from Nowruz 1404 = 21 Mar 2025 with 31/30-day months; Saka from Chaitra 1 = 22 Mar 2025; JDN = Python date.toordinal() + 1721425.
Where does the method come from?
E. G. Richards, “Calendars”, Explanatory Supplement to the Astronomical Almanac, 3rd ed. (2013), ch. 15; Unicode CLDR / ICU calendars (islamic-umalqura, islamic-civil, hebrew, persian, indian); E. M. Reingold and N. Dershowitz, Calendrical Calculations, 4th ed. (2018).