Quick answer
On 7 November 2026, someone born on 14 May 1990 has lived 13,326 days. Their physical cycle is at +63% and falling, their emotional cycle is at -43% and rising, and their intellectual cycle is at -91% and rising. The next critical day is emotional, on Monday, 9 November 2026.
The Biorhythm Calculator shows where you are in the three classic biorhythm cycles on any day: physical (23 days), emotional (28 days) and intellectual (33 days), with a chart of the 15 days either side. Biorhythms are a popular idea from the early 20th century, not science, so treat the result as fun.
How to Use the Biorhythm Calculator
Type in your birth date: the day and month, then the year. Leave “Date to check” empty to use today, or fill it in to check another day. Select Calculate. Two quick chips sit below the form: 14 May 1990 and 1 January 2000. Each one calculates at once.
Leave the birth date blank and the tool replies: “Enter the date of birth.” An impossible date brings up: “One of the dates is not valid. Please check it.” A date to check before the birth date is refused with: “The date to check is before the date of birth.”
The result shows each cycle as a percentage from -100% to +100%. The big line names the highest cycle, for example “Physical cycle highest (63%)”, and the line underneath reads “Day 13,326 of your life, Saturday, 7 November 2026 (today).
Positive values are the high phase of a cycle, negative the low phase.” The chart shows the 15 days before and after the day you chose, marked by the dashed line. Below the chart, a note reads “Biorhythms are a popular idea, not science: studies have not found that they predict performance or events.
Next zero-crossing (“critical”) days: Emotional on 9 November 2026; Intellectual on 13 November 2026; Physical on 21 November 2026.” When no critical day falls in the next 30 days, the note ends “none in the next 30 days” instead.
For star-sign matching, try the Zodiac Compatibility calculator. The Your Life in Numbers calculator shows how many hours of sleep you have had in your life so far.
The Three Cycles
Each cycle starts at zero on the day you were born and follows a smooth wave: it rises to a high point, falls back through zero, reaches a low point and returns to zero.
| Cycle | Length | Traditionally linked to | Peak | Zero crossings | Critical days per year |
|---|---|---|---|---|---|
| Physical | 23 days | Strength, energy, coordination | 5.75 days in | Every 11.5 days | About 31.8 |
| Emotional | 28 days | Mood, sensitivity, creativity | 7 days in | Every 14 days | About 26.1 |
| Intellectual | 33 days | Memory, alertness, reasoning | 8.25 days in | Every 16.5 days | About 22.1 |
How the Values Are Calculated
The calculator counts the days you have lived, then uses the sine function for each cycle: value = sin(2π × days lived ÷ cycle length).
The result runs from +1 (+100%), the top of the high phase, to -1 (-100%), the bottom of the low phase. A value near zero means the cycle is crossing between phases.
Because 23, 28 and 33 have no common factor, the three cycles only all start together again after 21,252 days, about 58 years. For someone born on 14 May 1990, that next reset is Monday, 20 July 2048, in 7,926 days from 7 November 2026.
The tool does not show whether each cycle is rising or falling, or which day of the cycle you are on, so the guide gives both here.
A cycle is rising while its value climbs toward the peak and falling while it drops toward the low point. The day-in-cycle is the remainder plus one: a remainder of 9 means day 10 of 23.
Worked Example
Someone born on 14 May 1990 has lived 13,326 days on 7 November 2026. Dividing by each cycle length shows where each wave is: Physical: 13,326 ÷ 23 leaves a remainder of 9 days into the cycle, day 10 of 23, at +63% and falling.
Emotional: 13,326 ÷ 28 leaves 26 days, day 27 of 28, at -43% and rising. Intellectual: 13,326 ÷ 33 leaves 27 days, day 28 of 33, at -91% and rising. The big line reads “Physical cycle highest (63%)”. The calculator turns these positions into percentages and draws the curves.
The Next 90 Days
The tool draws only 15 days either side of the date you check, so the guide gives the values further out, at 30, 60 and 90 days ahead:
| Date | Physical | Emotional | Intellectual |
|---|---|---|---|
| 7 November 2026 (today) | +63%, falling | -43%, rising | -91%, rising |
| 7 December 2026 (+30 days) | -94%, falling | 0%, rising (critical day) | -99%, falling |
| 6 January 2027 (+60 days) | 0%, rising (critical day) | +43%, rising | -76%, falling |
| 5 February 2027 (+90 days) | +94%, falling | +78%, rising | -28%, falling |
The first day when all three are above +50% is Monday, 3 May 2027, in 177 days, with values of +52%, +100% and +91%. No day in the next 300 days has all three above +90%.
Critical Days
Biorhythm theory calls the days when a cycle crosses zero “critical days”, supposedly times of instability. The calculator lists the next ones within 30 days, at most three.
For someone born on 14 May 1990, as of 7 November 2026, they are: Emotional on Monday, 9 November 2026, in 2 days; Intellectual on Friday, 13 November 2026, in 6 days; Physical on Saturday, 21 November 2026, in 14 days.
Two more fall inside the 30 days but past the three shown: Emotional again on Monday, 23 November 2026 and on Monday, 7 December 2026, because the emotional cycle crosses zero every 14 days.
The 28-day emotional cycle crosses zero on whole days, at the restart and at the halfway point.
The 23 and 33-day cycles cross zero at the restart only: their halfway crossings, 11.5 and 16.5 days into the cycle, fall between two days, so the tool does not list them. The listed days are exact, the days a cycle restarts at zero, not approximate.
Biorhythm Compatibility
Some people compare two people’s charts: when two cycles are in step, the theory says the pair feel alike in that area. You can check this yourself by calculating both people’s biorhythms for the same day.
On 7 November 2026, born 14 May 1990 gives Physical +63%, Emotional -43%, Intellectual -91%. Born 1 January 2000 gives Physical +63%, Emotional +100%, Intellectual +91%. The physical values are identical because the age difference, 3,519 days, is exactly 153 times 23.
The emotional values differ by 143 points and the intellectual by 182, out of a possible 200. The theory would call this pair in step physically and out of step emotionally and intellectually. The evidence says the match means nothing either way.
Birth Time
The tool counts whole days from the birth date, so a birth time is not an input.
A birth time would shift each value by at most about 14 percentage points for the physical cycle, the shortest, 11 for the emotional and 10 for the intellectual, and usually much less, because half a day is a small part of a 23-day wave. The date alone is enough for the tool’s purpose.
What the Evidence Says
Biorhythm theory was developed around 1900 by Wilhelm Fliess and Hermann Swoboda and became popular in the 1970s. Researchers have tested it many times, for example against accident records and sports results, and have not found that biorhythms predict performance, accidents or mood better than chance.
The most cited review is by the psychologist Terence Hines, published in Psychological Reports in 1998.
He examined 134 biorhythm studies, published and unpublished: 35 reported some support, but a closer look explained them by errors in method and statistics, and the other 99 found no support. His conclusion was that biorhythm theory is not valid.
One of the largest tests looked at accidents. Nijsten and Willemsen (1991) compared birth dates with accident dates for 29,085 trauma patients seen at the University Hospital of Groningen in the Netherlands between 1981 and 1983, and 930 seriously injured patients admitted there between 1985 and 1989.
Accidents were not more frequent on critical days. Real body rhythms do exist, such as the 24-hour circadian rhythm and the menstrual cycle, but they are not the fixed cycles that start at birth described here. So use the calculator as entertainment or a conversation starter, and do not plan anything important around it.
Real Rhythms You Can Track
If you are interested in rhythms that are backed by evidence, the 24-hour circadian rhythm governs sleep and alertness, and regular sleep and wake times are linked to better health and concentration. The Your Life in Numbers calculator shows how many hours of sleep you have had in your life so far.
Reading Your Chart
The chart shows the 15 days before and after the day you chose, marked by the dashed line. Each coloured line is one cycle: green for physical, gold for emotional, blue for intellectual.
Where a line is above the middle, that cycle is in its high phase; below it, the low phase. Where lines cross the middle, the theory places a critical day. Because the cycles have different lengths, they drift in and out of step.
Sometimes all three are high together, sometimes all low, and most of the time they are mixed. People who enjoy biorhythms often look for the rare days when all three peak together, which the theory treats as especially good days.
Where the Cycle Lengths Come From
Wilhelm Fliess, a Berlin physician, proposed the 23-day and 28-day cycles around 1900, and the 33-day intellectual cycle was added in the 1920s by Alfred Teltscher, an Austrian teacher. The numbers were chosen from observation and belief rather than measurement, which is one reason later research did not support them.
How This Calculator Compares
Three biorhythm calculators rank for the same query, and each one shows the same three cycles a little differently. The table below shows them next to each other.
| Feature | This page | Roberin | TheAstroAcademy | Quantum Biorhythm |
|---|---|---|---|---|
| Free, no download, no sign-up, no account | Yes | Yes | Yes | Yes, with paid extras |
| Physical, emotional and intellectual cycles | Yes | Yes | Yes | Yes |
| Percentages from -100% to +100% | Yes | Yes | Yes | Yes |
| Rising or falling direction | No, in the guide | Yes | No | Yes |
| Day-in-cycle | No, in the guide | Yes | No | Yes |
| Chart 15 days either side | Yes | Yes | Yes | Yes |
| Critical days, next 30 days | Yes | Yes | Yes | Yes |
| Intuitive 38-day cycle | No | No | Yes | Yes |
| More cycles (aesthetic, awareness, spiritual) | No | No | No | Yes |
| Compatibility tool | No, in the guide | Yes, separate page | Yes | Yes |
| 90-day or longer forecast | No, in the guide | No | No | Yes, 365 days |
| Average of the three cycles | No | Yes | Yes | Yes |
Where this page stops: it shows no rising or falling direction, no day-in-cycle, no 90-day chart, no birth time and no compatibility tool. Roberin shows the direction and the day-in-cycle, Quantum Biorhythm adds four more cycles and a 365-day forecast, and TheAstroAcademy adds the intuitive cycle.
What only this guide gives you is the 90-day values table, the birth-time shift and the worked compatibility example, all worked by hand in the guide above.
Keep Exploring
Zodiac Compatibility Calculator: see how two star signs match, with the aspect score behind it.
Your Life in Numbers: count the heartbeats, breaths and hours of sleep in your life so far.
Moon Phase Calculator: find the phase of the Moon on any date, with the age and the light.
Chinese Zodiac Finder: find your Chinese zodiac animal from your birth date and the Lunar New Year rule.
Sources
Hines, T. M. (1998), “Comprehensive Review of Biorhythm Theory”, Psychological Reports (a review of 134 biorhythm studies, published and unpublished, concluding that the theory is not valid)
Wikipedia: Biorhythm (pseudoscience) (the history of the theory, from Fliess to the 1970s, and the evidence against it)
Frequently Asked Questions
What are the three biorhythm cycles?
Physical (23 days), emotional (28 days) and intellectual (33 days), each starting at zero on the day you were born.
Are biorhythms scientific?
No. Studies have not found that biorhythms predict performance, accidents or mood. They are best treated as entertainment.
What is a critical day?
A day when a cycle crosses zero, between its high and low phases. The theory says these days are unstable, but there is no evidence for it.
Why does my chart change every day?
Each cycle moves forward one day at a time, so the values change daily and repeat every 23, 28 and 33 days.
Can I check a past or future date?
Yes. Open “Date to check” and choose any date after your date of birth.
Why do the cycles start at birth?
Biorhythm theory assumes all three cycles begin at zero at the moment of birth and run unchanged for life. Real biological rhythms do not work this way, which is part of why the theory is not accepted.
Can biorhythms tell me when to plan important events?
No. There is no evidence that biorhythms affect outcomes, so plan important events around real factors like rest, preparation and availability.
Does my birth time matter?
Not to this calculator. It counts whole days from the birth date, so a birth time is not an input. A birth time would shift each value by at most about 14 percentage points, and usually much less.
Can I compare two people’s biorhythms?
Yes. Calculate both people for the same day and compare the three values. The guide gives a worked example: born 14 May 1990 and born 1 January 2000 share the same physical value on 7 November 2026, but differ by 143 points emotionally and 182 intellectually.