The two sides, and the third chart

The Design calculation is what separates a bodygraph from every other kind of birth chart. No astrological tradition computes a second set of positions from three months before you were born and prints it alongside the first. It is also why a Human Design chart carries 26 activations rather than 13. The Dream Rave is a third calculation again, using lunar rather than solar movement, and it is not printed on a standard chart.

Degrees, not days

The Design side is often described as 88 days before birth, and that is a good working approximation that is not quite what happens. The measurement is 88 degrees of solar arc, and because the Earth does not move around the Sun at a constant rate, that arc takes a slightly different number of days depending on the time of year. The software resolves it from an ephemeris. You do not need to, and you should be a little suspicious of anyone who quotes the day count as though it were exact.

The wheel the gates sit on

The 64 gates are mapped around a 360-degree wheel, the mandala, with the I Ching hexagram sequence laid against the zodiac. Every planetary position in your chart is a degree on that wheel, and reading it off gives a gate, then a line within the gate, then a color, tone and base beneath that. Six subdivisions deep, all of it from one number.

Those positions are tropical. The tropical zodiac is anchored to the seasons, to the vernal equinox rather than to the constellations, and it is what carries the gate, line, color, tone and base locations on the wheel. This is not a preference. It is the frame the system was transmitted in and the frame its numbers refer to.

Where Vedic astrology does come in

Human Design does carry both. The tropical layer is what produces the individual chart, the psychology, and every activation on the wheel. The Vedic layer is associated with the larger global cycles rather than with your own mechanics. So the honest answer to whether this is a tropical or a Vedic system is that it uses both, at different scales, and the one that decides your Type is tropical.

Which is why picking a zodiac is not a thing a Human Design student needs to do. If you also study astrology, the question of which frame to work in is a real and interesting one. It is a question inside astrology, not a setting on your bodygraph.

Houses, aspects and the rest of the astrological toolkit

Houses divide the sky relative to the horizon at your birthplace, and there are more than a dozen ways to do it. Aspects measure the angles between planets. Both are real techniques answering real questions, and neither feeds a bodygraph. Nothing in Human Design is computed from a house cusp or from a trine. Where this site works with astrological material, in medical astrology and in decumbiture, the two layers are kept visibly separate for that reason.

How fast the program moves

The speeds are worth knowing, because they explain why your birth time matters as much as it does and why most transits pass without registering.

Approximate, and retrograde movement is not accounted for here. The Moon crossing a line in about ten hours is the reason an hour of birth-time error can change a chart, and the reason the birth time page exists.

Common questions

Is Human Design tropical or sidereal?

The positions that produce your bodygraph are tropical. Every gate, line, color, tone and base is located on the mandala wheel using the tropical zodiac, which is why changing to a sidereal calculation does not give you a different Human Design chart, it gives you something that is no longer a Human Design chart. The system does also carry a Vedic layer, which is associated with the larger global cycles rather than with individual chart mechanics.

What are the 88 degrees?

Your chart is two calculations, not one. The Personality side, printed in black, is taken at the exact moment of birth. The Design side, printed in red, is taken when the Sun was 88 degrees of arc earlier, which works out at roughly 88 days before you were born. That second calculation is what makes a bodygraph different from a birth chart in any other system.

Why does the Design side use 88 degrees and not 88 days?

Because the measurement is of solar arc rather than of calendar time. The Earth does not travel at a constant speed around the Sun, so 88 degrees of movement takes slightly different numbers of days depending on when in the year you were born. Roughly three months is the useful approximation. The calculation itself is degrees.

Do house systems change a Human Design chart?

No. Houses are an astrological layer and the bodygraph does not use them. Placidus, Koch, Whole Sign and the rest divide the sky relative to the horizon at your birthplace, which is a real technique answering real astrological questions. None of it feeds the gates, the centers, your Type or your Authority.

Why does my birth time matter so much?

Because the fast-moving bodies change gate and line inside hours. The Moon crosses a gate in about thirty hours and a line in about ten, so an hour of error can move it. Type, Authority, Definition and Profile are the values people care about most, and they are the ones most likely to flip on a bad time. There is a full treatment of how much error each value tolerates on the birth time page.

Will different software give me different charts?

For the same birth data, properly entered, no. Reputable Human Design software agrees, because the ephemeris and the 88-degree rule are not matters of opinion. Disagreements almost always come from the birth data itself: a timezone applied wrongly, a daylight saving rule missed, or a birth time rounded to the hour on a certificate.