Physical, emotional, and cognitive cycles with circadian rhythms
Your biorhythm is the one reading here built from arithmetic rather than a wisdom tradition. From your date of birth alone, the calculator plots sine waves that all begin at zero on the day you were born and repeat on fixed cycles: physical every 23 days, emotional every 28, intellectual every 33. It reads out where each wave sits today, flags the critical days when a cycle crosses zero, and projects a short forecast so you can see the rhythm arriving before it does.
Give it your date of birth and it counts the exact number of days you have been alive, then places that count on each cycle's wave. Three primary cycles drive the main read: physical (23 days), emotional (28 days), and intellectual (33 days). Four longer secondary cycles sit alongside them for the curious: intuitive (38), aesthetic (43), awareness (48), and spiritual (53). Each returns a level that swings from its low to its high, shown as a percentage with a rising or falling trend and a plain phase label like peak, neutral, or valley. You never need a birth time here, only the calendar date.
Every cycle is a single sine wave, computed as the sine of two pi times your days alive divided by the cycle's period. On your birthday all of them sit exactly at zero and start climbing together. Each cycle then spends roughly half its span above the midline, the charged half, and half below it, the recharging half. Because the periods differ, the three primary waves almost never line up, and that mismatch is what makes any given day's blend of energy unique to that date. The output is fully deterministic, so the same birth date and day always produce the same chart.
A critical day is the moment a cycle crosses zero and flips from charged to recharging, traditionally read as a less steady, lower control window rather than a bad omen. The engine surfaces the next critical days across your cycles, marks the peak days when a wave nears the top of its range, and rolls the whole picture into a seven day forecast with an overall composite level. It also offers an event analysis: drop in a past date, an exam, a race, a hard conversation, and see the cycle state you were actually in that day. This is where the chart becomes a mirror for patterns you already remember.
This reading is candid about its own footing. The classic 23, 28, and 33 day periods trace back to Fliess, Swoboda, and Teltscher, and they were never confirmed as a universal biological law. Broad reviews, including Hines in 1998, found no consistent population wide predictive power in the original model, and the engine says so on each section with evidence badges you can open to read the studies. What it layers on top is real chronobiology, and it can calibrate the cycles to your own logged mood and energy, testing whether a cycle genuinely tracks your patterns before it counts toward anything. Treat it as a reflective self awareness tool, not medical or professional advice.
Beyond the birth cycles, you pick your chronotype (Lion, Bear, Wolf, or Dolphin, following Michael Breus) and set your usual wake time. The engine blends your chronotype's hourly alertness curve with today's cycle energy to suggest the best hours for physical effort, focused thinking, creative work, and emotional conversations. It extends the same logic into sleep timing and eating windows. This chronotype and circadian layer is the part grounded in mainstream research, distinct from the older sine model, which is why it carries the stronger evidence framing.
The three primary cycles only realign perfectly at their common multiple, 21,252 days, which works out to about 58.2 years. The calculator calls this the Grand Cycle and shows where you currently sit within that long arc. Add a second date of birth and it computes biorhythm compatibility, overlaying both sets of waves to find shared high energy windows, days of likely friction, and the critical days you would both be navigating at once. It is a light, playful way to compare two rhythms rather than a verdict on a relationship.
The calculator takes your date of birth, counts how many days you have been alive, and feeds that number into a sine wave for each cycle. The formula is the sine of two pi times your days alive divided by the cycle length in days. Nothing about your birth time, location, or star sign is involved, so it is pure arithmetic on the calendar.
Three primary cycles carry the main reading: physical over 23 days, emotional over 28 days, and intellectual over 33 days. Four longer secondary cycles are also shown for interest: intuitive, aesthetic, awareness, and spiritual. The primary three are the ones that drive the everyday level and the critical day alerts.
A critical day is the day a cycle passes through zero, switching from its charged half to its recharging half. In the classic tradition these were read as less stable, lower control moments rather than disasters. The engine flags upcoming critical days so you can notice them, but it frames them as reflective heads ups, not predictions of harm.
The classic 23, 28, and 33 day periods were never validated as a universal biological law, and reviews such as Hines in 1998 found no population wide predictive effect, which the engine states openly. The chronotype and circadian rhythm layer it adds on top is drawn from mainstream chronobiology, and the engine can also test the cycles against your own logged data. Use it as a self awareness tool, not medical advice.
No. This engine uses only the calendar date of your birth, so a rough or unknown birth time makes no difference to the result. Birth time matters for other readings on the site, but the biorhythm chart ignores it entirely.
Yes. Enter a second date of birth and the engine overlays both people's cycles to produce a compatibility view. It highlights shared high energy windows, days where your rhythms are likely to clash, and the critical days you would both be moving through at the same time.
Your chronotype is your natural body clock type, described here as Lion, Bear, Wolf, or Dolphin after Michael Breus. The engine combines it with today's cycle energy to suggest your best hours for exercise, focus, creativity, and rest. It is the circadian science layer that sits beside the older sine wave model.