Interactive cycle explorer
Calendar Round
Calculator
Explore how the 260-day Tzolk’in and 365-day Haab interlock to create a unique 18,980-day cycle.
01 Choose a date
Find its Calendar Round
Convert a Common Era Gregorian date into its paired cycles.
01 Build a combination
Find its occurrences
Choose both calendar positions and a Gregorian reference date.
Least common multiple
LCM(260, 365) = 18,980 days
02 Read the cycle
Calendar Round date
1 Ik’ · 15 Mol Day 16,963 of 18,980Occurrences around the reference
Same combination, one full round later
Two cycles, one repeating date. A Calendar Round identifies a day uniquely within about 52 years.
Why the wheels meet
An interlocking calendar
Tzolk’in
13 × 20 = 260Thirteen numbers turn through twenty named days, producing 260 distinct sacred-calendar positions.
Haab
18 × 20 + 5 = 365Eighteen periods of twenty days are followed by the five-day Wayeb period.
Calendar Round
LCM(260, 365) = 18,980The paired date returns only when both cycles reach the same relative position again.
Pairing rules
Not every combination is possible
Because both 260 and 365 are divisible by five, only one-fifth of the nominal Tzolk’in and Haab pairings occur in the interlocked sequence. This calculator checks that shared five-day alignment before finding a position.
A Calendar Round date repeats every 18,980 days. To distinguish events separated by more than one round, Maya scribes could use the Long Count, which records a longer chronological position.
Learn from the source