About CycleCalcs

CycleCalcs is a growing home for the study of cycles. It began as a few fast, free calculators and has grown to include a sorted reference of astronomical cycles and interactive lessons on how the sky's rhythms work. They are handy for everyday date math and numerology, and for anyone exploring the larger rhythms of time and the sky.

What's here

• Date Calculator: add or subtract years, months, weeks and days, or measure the exact span between two dates.
• Synodic Period Calculator: the alignment period of two bodies, and the multi-body realignment cycle for three or more.
• Pythagorean Numerology Calculator: add up the classic Pythagorean letter values of words and names.
• Cycles by Length: a sorted reference of astronomical and natural cycles, from a single day to the galactic year.
• Learn: interactive, plain-language lessons on Moon phases, eclipses, the lunar nodes, the seasons and the precession of the equinoxes.

A note on accuracy

The calculators aim to be correct and transparent, but they're provided for general educational and research use. They are not professional financial, investment, legal, or astrological advice. Orbital periods use standard mean values; numerology is an interpretive tradition, not science.

Questions or corrections? See the Privacy Policy for contact details.