Thirteen months of twenty-eight days each — built on logic, symmetry and
the rhythms of nature.
↓ explore the system ↓
The system
Pure logic, eternal symmetry
Our current Gregorian calendar has grown over centuries of history and
politics — filled with unequal months, shifting weekdays and illogical
leap days. This is an alternative: a year of thirteen months, each
identical.
13
months
per year
28
days
per month
4
weeks
exactly, always
364
year days
+ 1 special day
"Since every month is identical, you never need to remember which
weekday a date falls on. The 1st of every month is always Monday."
The year begins on 1 Ceres, the first spring month,
anchored to the vernal equinox — the moment when light returns, plants
grow and nature restarts. Many ancient calendars — Babylonian, Persian,
Celtic and the original Roman system — also began in spring.
The thirteen months
Each season, its own language
Spring
I
Ceres
Awakening — beginning, seed, potential
20 Mar – 16 Apr
II
Dalia
Growth — direction, movement, form
17 Apr – 14 May
III
Eos
Light — clarity, vision, insight
15 May – 11 Jun
Summer
IV
Flora
Bloom — creation, beauty, abundance
12 Jun – 9 Jul
V
Gaia
Life — stability, strength, vitality
10 Jul – 6 Aug
VI
Helia
Sun — peak, warmth, connection
7 Aug – 3 Sep
Autumn
VII
Iris
Transition — balance, change, gratitude
4 Sep – 1 Oct
VIII
Juno
Harvest — result, gathering, appreciation
2 Oct – 29 Oct
IX
Krona
Time — release, rhythm, wisdom
30 Oct – 26 Nov
Winter
X
Luma
Silence — rest, introspection
27 Nov – 24 Dec
XI
Mira
Dream — imagination, mystery
25 Dec – 21 Jan
XII
Aurora
Hope — expectation, light
22 Jan – 18 Feb
XIII
Bruma
Closure — ending, completion
19 Feb – 18 Mar
Always the same grid
A month page that never changes
Since every month spans exactly four weeks and always starts on Monday,
every month page looks identical. No irregular rows, no 29, 30 or 31
days — always exactly 28.
Ceres
I
Awakening — beginning, seed, potential
20 Mar – 16 Apr
Mon
Tue
Wed
Thu
Fri
Sat
Sun
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Every month looks like this — day 1 is always Monday, day 28 always
Sunday. The calendar never needs to be adjusted.
✦
Day of Creation
The timeless transition day at the end of every year — not a
Monday, not a Sunday. A moment of reflection, gratitude and
intention, before the new year begins.
Every year
✦✦
Day of Renewal
In a leap year, a second special day follows — also outside the
week. A cosmic correction: the earth takes a breath, the rhythm is
restored.
Leap Year
The leap year system
One elegant solution to an astronomical problem
A tropical solar year lasts about 365,2422 dagen. days. A 13-month calendar
totals 364 days plus one special day, making 365 dagen days. This leaves a
difference of roughly 0.2422 days per year, which accumulates to about
one full day every four years. Without correction, the spring equinox
would gradually drift, causing the calendar to lose its alignment with
astronomical seasons.
Regular year
364 days13 × 28
✦Day of Creation
= 365 days
every ~4 years
Leap Year
364 days13 × 28
✦Day of Creation
✦✦Day of Renewal
= 366 days
"Both special days fall outside the week structure and outside the
months. The week structure remains completely unaffected — 1 Ceres
always stays Monday."
Two approaches are possible for determining the leap year:
⚙
Gregorian rule
Practical
Divisible by 4 → leap year
But divisible by 100 → not a leap year
Unless also divisible by 400 → still a leap
year
The same rule as the Gregorian system — already precisely calibrated
to the same astronomical problem, and easy to adopt.
✦
Equinox-coupled
Astronomically pure
Does the equinox threaten to shift? → add Day of Renewal
Directly rooted in the movement of the earth itself. Perfectly
aligned with the philosophy of the calendar: the rhythm of nature as
the sole authority.
Celebrations
Holidays rooted in nature
Without the arbitrariness of historical politics: the holidays mark
astronomical and seasonal moments that are universally recognisable.
New Year
Day of Creation · 19/20 Mar
Transition moment between cycles
Spring Festival
1 Ceres · 20/21 Mar
Start of the new year
Earth Day
1 Gaia · 10 Jul
Summer, strength, nature
Midsummer
14 Helia · 20 Aug
Peak of the light
Autumn Festival
1 Krona · 30 Oct
Beginning of harvest and reflection
Midwinter
14 Luma · 10 Dec
Light in the darkness
Date Converter
Translate any date to the new system
Enter a Gregorian date to find the corresponding 13-month date — or
vice versa. You can also directly see what day today is.
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—
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"The Gregorian calendar is a product of history and politics. This
calendar is a product of logic and nature."