Why Are There 12 Months?

There are some things in our day-to-day lives that we just take for granted: the time on a clock. The seasons of the year. The months on a calendar.

But why are these things the way they are? Why are there 12 months in a year, instead of 13? What is a lunar month, and how many of those fit into our standard calendar year?

As the experts in all things calendars, we’re here to clear up any confusion surrounding the months in a year, and help you to understand how our current system – known as the Gregorian calendar – works.

Why are there 12 months in a year?

The concept of there being 12 months in a year dates back to the Romans. In 738 B.C., the Romans started with a 10-month calendar, which was borrowed from the Greeks. This consisted of:

Martius
Aprilis
Maius
Junius
Quintilis
Sextilis
September
October
November
December

However, these 10 months didn’t fully account for the 365.25 days that it takes for the earth to orbit the sun. This misalignment was challenging for agricultural workers, as the months of the year and seasons didn’t line up with the condition of their crops.

As a result, Januarius and Februarius were later added to the end of the year, which would account for the remaining 60 days and go towards making the calendar what we recognise today.

In 46 B.C. (nearly 700 years later), Julius Caesar changed the calendar so every month would have 30 or 31 days – apart from Februarius, which had 29 days – and the calendar year would now start with Janaurius.

This shifted the months into an order that’s identical to what we use today (albeit with modernised names).

Why can’t we have 13 months a year, instead of 12?

While the Gregorian calendar contains 12 months in a year, various proposals throughout history have suggested other methods of measuring a lunar cycle.

One of these ideas is the International Fixed Calendar (IFC), which was theorised by Moses Cotsworth in 1902. The IFC would have 13 months, each comprised of 28 days. The months would start on a Sunday and end on a Saturday, with a one-day public holiday between the last Saturday of the year and January 1st.

The reason why other calendars haven’t been widely adopted is largely down to tradition. The Gregorian calendar and its 12 months a year are cemented into everyday life, impacting:

Work patterns
Seasonal farming and harvests
Annual celebrations, like birthdays or public holidays

Changing to a 13-month system would require an international overhaul unlike we’ve ever seen!

Gregorian calendar Vs. Islamic calendar

While the Gregorian calendar – with its 12 months and 365 days a year – is the most common calendar used in the Western world, there are other calendars used globally.

One of these is the Islamic calendar, also known as the Hijri calendar or Arabic calendar. This is a lunar calendar consisting of 12 lunar months, in a year of 354 or 355 days. It’s used to recognise the correct days of Islamic holidays and rituals.

Traditionally, days according to the Islamic calendar start and end at sunset. Months commence on the birth of a new lunar cycle, so each month may have 29 or 30 days based on the visibility of the moon.

Find the perfect calendar for you

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