∿ Free Biorhythm Calculator: Physical, Emotional & Intellectual

Umbriel plots your three biorhythm curves free, centred on today: physical (23 days), emotional (28) and intellectual (33), running from the day you were born.

The idea dates to the late nineteenth century and was popular enough by the 1970s to appear in newspapers and pocket calculators. Count the days since your birth, feed that into three sine waves of different lengths, and you get three curves: physical stamina, emotional steadiness and intellectual sharpness, each swinging from +100% to -100%.

Days when a curve crosses zero are called critical days in the literature and were treated as the notable ones. When all three happen to align (which takes 21,252 days, around 58 years) enthusiasts made rather a lot of it.

It has been tested, repeatedly, and it does not hold up. There's no evidence that these cycles predict anything. Umbriel includes it because it's a charming piece of early-twentieth-century thinking and the maths is real even if the theory isn't, and because a wave showing where you are in a rhythm is a surprisingly nice prompt to check in with yourself. We'd rather say that plainly than dress it up.

This tool plots three sine waves that start on the day you were born: a 23-day physical cycle, a 28-day emotional cycle and a 33-day intellectual cycle. Umbriel counts the whole days between your birth date and today using Julian Day Numbers, then evaluates sin(2 x pi x days / period) for each cycle, so +100 percent is the peak and -100 percent the trough. A cycle is labelled critical when its rounded value is within 15 percent of zero, and rising or falling by comparing today's value with yesterday's. The next crossing of zero for each cycle is found by stepping forward day by day through the same formula, for up to 40 days, and the next day on which all three are above 0.6 is searched for up to 400 days ahead, so the dates printed match the curve drawn. Only your birth date is used; time, place and zodiac play no part. Biorhythm is a symbolic model from the early twentieth century that layers fixed periods onto a date. It is not astronomy and it has no measurement behind it, so there is no accuracy figure to quote: the arithmetic is exact and what it says about your energy is not established.