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What is the Shamsi (Persian) Calendar? — A Complete Guide

Everything you need to know about the Solar Hijri calendar — its origins, structure, months, and why it remains one of the most accurate calendars in the world.

What Is the Shamsi Calendar?

The Shamsi calendar is the official calendar of Iran and Afghanistan. Its formal name is the Solar Hijri calendar (abbreviated SH), and it is also widely known as the Jalali calendar, the Persian calendar, or simply the Iranian calendar. The word "Shamsi" (شمسی) literally means "solar" in Persian and Arabic, distinguishing it from the Lunar Hijri (Qamari) calendar used in much of the Arab world.

The Shamsi calendar is a solar calendar — meaning it tracks the Earth's revolution around the Sun — and its year begins precisely at the moment of the vernal equinox (the March equinox), which is the astronomical start of spring in the Northern Hemisphere. This moment marks Nowruz (نوروز), the Persian New Year, one of the oldest continuously celebrated holidays in the world.

Because the Shamsi new year is pinned to an actual astronomical event rather than an arbitrary date, it is considered one of the most astronomically accurate calendars in active use today. The year typically begins on March 20 or 21 of the Gregorian calendar.

A Brief History of the Persian Calendar

Ancient Roots

The history of the Persian calendar stretches back over 3,000 years to the ancient Zoroastrian traditions of the Iranian plateau. The earliest known Persian calendars were used during the Achaemenid Empire (550–330 BCE), the dynasty of Cyrus the Great and Darius I. These ancient calendars were solar in nature and contained 12 months of 30 days each, with five extra "Gatha" days added at the end of the year to account for the full solar cycle.

Through the centuries — including the Seleucid, Parthian, and Sassanid periods — the Persian calendar underwent various modifications. The Sassanid-era calendar (224–651 CE) had a sophisticated intercalation system, though it gradually drifted from the astronomical year over time.

The Khayyam Reform (11th Century)

The most significant reform in the history of the Persian calendar occurred in 1079 CE under the Seljuk Sultan Jalal al-Din Malik-Shah I. The sultan assembled a committee of the finest astronomers of the age, including the legendary polymath Omar Khayyam (عمر خیام), to create a new, astronomically precise calendar.

The result was the Jalali calendar (تقویم جلالی), named after the sultan. Khayyam and his colleagues produced a calendar with a remarkably accurate measurement of the tropical year — approximately 365.2424 days. This was more precise than the Gregorian calendar (introduced 500 years later in 1582), which estimates the year at 365.2425 days. The Jalali calendar's error amounts to roughly one day every 3,770 years, compared to the Gregorian calendar's one day every 3,236 years.

Modern Standardization

The modern Solar Hijri calendar was formally adopted as Iran's official calendar on March 31, 1925, during the early Pahlavi dynasty. The calendar adopted the Hijri epoch (the migration of Prophet Muhammad from Mecca to Medina in 622 CE) but retained its solar calculation. In 1957, the Afghan government also officially adopted the Solar Hijri calendar, though with some differences in month names.

Structure of the Shamsi Calendar

The Shamsi calendar consists of 12 months totaling either 365 or 366 days. The structure follows a logical, astronomy-driven pattern:

• First 6 months: Each has 31 days — this corresponds to the longer period the Sun spends in the northern ecliptic during spring and summer
• Next 5 months: Each has 30 days — corresponding to the shorter autumn and early-winter period
• Last month: Has 29 days in a regular year and 30 days in a leap year

This pattern (6×31 + 5×30 + 29 = 365 days) is not arbitrary — it reflects the actual variation in the Earth's orbital speed. The Earth moves slower when it is farther from the Sun (around July, during the first half of the Shamsi year), so those months appear to be "longer."

The 12 Months of the Shamsi Calendar

Below is the complete list of all twelve months, with their English transliteration, Farsi name, approximate Gregorian equivalent, and number of days:

#	English Name	Farsi Name	Approx. Gregorian	Days
1	Farvardin	فروردین	Mar 20 – Apr 19	31
2	Ordibehesht	اردیبهشت	Apr 20 – May 20	31
3	Khordad	خرداد	May 21 – Jun 20	31
4	Tir	تیر	Jun 21 – Jul 21	31
5	Mordad	مرداد	Jul 22 – Aug 21	31
6	Shahrivar	شهریور	Aug 22 – Sep 21	31
7	Mehr	مهر	Sep 22 – Oct 21	30
8	Aban	آبان	Oct 22 – Nov 20	30
9	Azar	آذر	Nov 21 – Dec 20	30
10	Dey	دی	Dec 21 – Jan 19	30
11	Bahman	بهمن	Jan 20 – Feb 18	30
12	Esfand	اسفند	Feb 19 – Mar 19	29/30

How Does the Shamsi Calendar Differ from the Gregorian Calendar?

Both the Shamsi and Gregorian calendars are solar calendars — they both track the Earth's orbit around the Sun and have approximately 365.25 days per year. However, they differ in several important ways:

• Epoch (Starting Year): The Gregorian calendar counts from the estimated birth year of Jesus Christ (1 AD). The Shamsi calendar counts from the year of the Hijra — Prophet Muhammad's migration from Mecca to Medina — in 622 CE. So the Gregorian year 2026 roughly corresponds to Shamsi year 1404–1405.
• New Year's Day: The Gregorian new year starts on January 1, which has no astronomical significance. The Shamsi new year starts at the precise moment of the vernal equinox (around March 20–21), making it astronomically anchored.
• Month Lengths: Gregorian months have an irregular distribution of 28, 29, 30, or 31 days. The Shamsi calendar follows a clean, logical pattern: 31-31-31-31-31-31-30-30-30-30-30-29(30).
• Accuracy: The Shamsi calendar's leap year system, based on astronomical observation, produces an average year length that is slightly more accurate than the Gregorian system.

How Does the Shamsi Calendar Differ from the Islamic (Lunar Hijri) Calendar?

The Shamsi calendar is sometimes confused with the Islamic Hijri calendar because both use the Hijra as their epoch. However, the two calendars are fundamentally different:

• Solar vs. Lunar: The Shamsi calendar is solar (365 or 366 days/year). The Islamic Hijri calendar is purely lunar (354 or 355 days/year), tracking the Moon's phases.
• Year Length Gap: Because the lunar year is about 11 days shorter than the solar year, the Islamic Hijri calendar "drifts" through the seasons over a 33-year cycle. The Shamsi calendar stays fixed to the seasons.
• Year Number Divergence: Despite starting from the same historical event, the calendars now show different year numbers. The Islamic Hijri year is currently around 1447, while the Shamsi year is around 1404–1405 — a difference caused by the shorter lunar year accumulating more years over the same period.
• Usage: The Islamic Hijri calendar is used for determining religious observances (Ramadan, Eid, Hajj) across the Muslim world. The Shamsi calendar is used for civil, administrative, and everyday purposes in Iran and Afghanistan.

Leap Years in the Shamsi Calendar

Leap years in the Shamsi calendar add one extra day to the last month (Esfand), making it 30 days instead of 29. The leap year calculation is based on precise astronomical observation of the vernal equinox.

In practice, the Shamsi calendar follows an approximate 2820-year grand cycle for leap year calculation. Within this cycle, leap years occur roughly every 4 years, but with specific adjustments. The most commonly used algorithm distributes 683 leap years across every 2820-year period, resulting in an average year length of approximately 365.24219 days — which is extraordinarily close to the actual tropical year of 365.24219 days.

A simplified rule of thumb: leap years typically fall every 4 years, similar to the Gregorian calendar. However, unlike the Gregorian system (which skips leap years in most century years), the Shamsi system uses a different correction pattern based on multiples within 2820-year cycles. In modern practice, the exact moment of the vernal equinox is calculated by the Institute of Geophysics at the University of Tehran, ensuring each year starts at precisely the right astronomical moment.

Countries That Officially Use the Shamsi Calendar

The Shamsi (Solar Hijri) calendar is the official calendar in two countries:

• Iran: The calendar is used for all civil, governmental, educational, and business purposes. All government documents, school schedules, bank transactions, and media references use Shamsi dates. Iranians commonly refer to it as the "Shamsi calendar" (تقویم شمسی) or "Jalali calendar" (تقویم جلالی).
• Afghanistan: The Solar Hijri calendar is also official, though some month names differ. For example, the second month is called "Sawr" (ثور) in Dari/Pashto rather than "Ordibehesht." The Afghan version of the calendar was adopted in 1957.

Beyond official usage, millions of Persian-speaking people in the diaspora — in the United States, Canada, the United Kingdom, Germany, Australia, Turkey, and the UAE — continue to use the Shamsi calendar for personal, cultural, and social purposes. It remains central to the celebration of Nowruz and other Persian holidays.

Why the Shamsi Calendar Matters Today

The Shamsi calendar is more than just a timekeeping system — it is a living connection to one of the world's oldest continuous civilizations. For over 80 million Iranians and 40 million Afghans, it structures daily life, from school semesters and fiscal years to wedding dates and birthday celebrations.

For the global Persian-speaking diaspora, the Shamsi calendar serves as a cultural anchor. Knowing that "today is the 2nd of Khordad" carries a sense of identity and belonging that a Gregorian date alone cannot provide. It connects people to the rhythms of the ancient Zoroastrian seasonal festivals, the poetry of Hafez and Rumi, and the shared traditions of Nowruz, Yalda Night, and Chaharshanbe Suri.

How Boshkeh Makes Working with the Shamsi Calendar Easy

If you work with the Shamsi calendar — whether you're an Iranian professional managing deadlines, a student tracking academic schedules, or a member of the diaspora staying connected to your cultural roots — Boshkeh is designed for you.

• Full Shamsi Calendar Support: Boshkeh displays Shamsi dates natively, so you can see today's date in both Shamsi and Gregorian at a glance.
• Automatic Date Conversion: Seamlessly convert between Shamsi, Gregorian, and Islamic Hijri dates without manual calculation.
• Persian Holidays & Events: All major Iranian and Afghan holidays — Nowruz, Sizdah Bedar, Yalda Night, Chaharshanbe Suri, and dozens more — are built in.
• Google Calendar Sync: Sync your Shamsi-based events with Google Calendar so your Persian holidays appear alongside your work meetings.
• AI-Powered Insights: Get cultural and historical context about each day's significance, powered by intelligent AI.
• Privacy-First Design: Your calendar data stays secure and private. No tracking, no ads.