★ Two hearts, three rhythms ★
Biorhythm Compatibility
Enter two birthdates to see how your physical, emotional and
intellectual cycles line up — the classic 23/28/33-day biorhythm reading.
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Both birthdates never leave this device.
No server, no tracking, no cookies, nothing saved. The calculation runs entirely
in your browser, and this page's security policy physically blocks all network
connections. You can disconnect from the internet and it still works.
Overall biorhythm match
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The three cycles
The three figures at the top are each cycle's phase alignment — how in-step the
two birth dates are within that cycle (100% if born a whole number of cycles apart, 0% if
exactly half a cycle apart), so they don't depend on any single day:
85–100% almost always in step ·
70–84% well aligned ·
55–69% mixed ·
below 55% often out of phase.
The day match beneath each chart is the same measure for the single reading date
only. In each chart the curves rise above the line on "high" days and dip below on "low"
days; a crossing of the centre line is a critical day.
How biorhythm compatibility works
Biorhythm theory models three cycles that are said to start at birth and repeat for life:
- Physical — a 23-day cycle: energy, stamina, strength, coordination.
- Emotional — a 28-day cycle: mood, sensitivity, creativity, intuition.
- Intellectual — a 33-day cycle: memory, alertness, focus, reasoning.
Each person's cycle on a given day is sin(2π × days since birth / period),
swinging between +100% (peak) and −100% (low). Two people born a whole number of cycles
apart ride each wave together; born half a cycle apart, one peaks while the other bottoms out.
Daily compatibility for a cycle is how close the two people's values sit on a given
day: 100% when they're at the same point, 0% when one peaks while the other
bottoms out. The headline figure shown for each cycle (physical, emotional and intellectual) is
the two cycles' phase alignment — 100% when the birth dates fall a whole
number of cycles apart (the waves rise and fall together) and 0% when they fall exactly
half a cycle apart (one peaks as the other bottoms out) — so it runs the full 0–100%
and doesn't depend on any single day. Beneath each chart we also show the day match for
the chosen reading date. The overall score is the average of the three cycles' figures.
More private, offline compatibility tools: